Parse EBNF: Difference between revisions
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{{draft task}}
[[Category:Recursion]]
{{clarified-review}}
;Task:
Write a program that can parse a grammar in Extended Backus–Naur Form ('''EBNF'''), and then parse something else according to the grammar.
The program is only required to decide whether or not the something else belongs to the language described by the grammar, but for extra credit, it can output a syntax tree.
See [[Parse EBNF/Tests|the tests]].
<br><br>
=={{header|ALGOL 68}}==
The source of the Algol 68 sample is somewhat largish, so is on a separate page on Rosetta Code here: [[Parse EBNF/ALGOL 68]].
{{out}}
<pre>
Valid EBNF: a/z: 'a' { a = 'a1' ( 'a2' | 'a3' ) { 'a4' } [ 'a5' ] 'a6' ; } 'z'
a: seq
literal "a1"
oneof
seq
literal "a2"
seq
literal "a3"
list
literal "a4"
opt
literal "a5"
literal "a6"
"a1a3a4a4a5a6" is valid according to a
"a1 a2a6" is valid according to a
"a1 a3 a4 a6" is valid according to a
**** Syntax error near "a1 a4 a5 a6"
"a1 a4 a5 a6" is not valid according to a
**** Syntax error near "a5 a5 a6"
"a1 a2 a4 a5 a5 a6" is not valid according to a
**** Unexpected text: "a7" at the end of source
"a1 a2 a4 a5 a6 a7" is not valid according to a
**** Syntax error near "your ad here"
"your ad here" is not valid according to a
Valid EBNF: Arithmetic expressions:
'Arithmetic expressions'
{
expr = term { plus term } .
term = factor { times factor } .
factor = number | '(' expr ')' .
plus = '+' | '-' .
times = '*' | '/' .
number = digit { digit } .
digit = '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9' .
}
expr: seq
rule term
list
rule plus
rule term
term: seq
rule factor
list
rule times
rule factor
factor: oneof
seq
rule number
seq
literal "("
rule expr
literal ")"
plus: oneof
seq
literal "+"
seq
literal "-"
times: oneof
seq
literal "*"
seq
literal "/"
number: seq
rule digit
list
rule digit
digit: oneof
seq
literal "0"
seq
literal "1"
seq
literal "2"
seq
literal "3"
seq
literal "4"
seq
literal "5"
seq
literal "6"
seq
literal "7"
seq
literal "8"
seq
literal "9"
"2" is valid according to Arithmetic expressions
"2*3 + 4/23 - 7" is valid according to Arithmetic expressions
"(3 + 4) * 6-2+(4*(4))" is valid according to Arithmetic expressions
**** Syntax error near "-2"
"-2" is not valid according to Arithmetic expressions
**** Unexpected text: "+" at the end of source
"3 +" is not valid according to Arithmetic expressions
**** Syntax error near " 3"
"(4 + 3" is not valid according to Arithmetic expressions
**** Expected "{", not "a"
Invalid EBNF: a = '1';
**** Expected "}", not "(eof)"
Invalid EBNF: { a = '1' ;
**** Expected "=", not "world"
Invalid EBNF: { hello world = '1'; }
**** Rule "bar" not defined
Invalid EBNF: { foo = bar . }
</pre>
=={{header|Go}}==
{{trans|Phix}}
<br>
A more or less faithful translation except that indices are 0-based rather than 1-based and so 1 less than in the Phix results.
<syntaxhighlight lang="go">package main
import (
"fmt"
"strings"
)
// type aliases for Phix types
type object = interface{}
type sequence = []object
var (
src []rune
ch rune
sdx int
token object
isSeq bool
err = false
idents []string
ididx []int
productions []sequence
extras sequence
results = [2]string{"pass", "fail"}
)
func btoi(b bool) int {
if b {
return 1
}
return 0
}
func invalid(msg string) int {
err = true
fmt.Println(msg)
sdx = len(src) // set to eof
return -1
}
func skipSpaces() {
for {
if sdx >= len(src) {
break
}
ch = src[sdx]
if strings.IndexRune(" \t\r\n", ch) == -1 {
break
}
sdx++
}
}
func getToken() {
// Yields a single character token, one of {}()[]|=.;
// or {"terminal",string} or {"ident", string} or -1.
skipSpaces()
if sdx >= len(src) {
token = -1
isSeq = false
return
}
tokstart := sdx
if strings.IndexRune("{}()[]|=.;", ch) >= 0 {
sdx++
token = ch
isSeq = false
} else if ch == '"' || ch == '\'' {
closech := ch
for tokend := sdx + 1; tokend < len(src); tokend++ {
if src[tokend] == closech {
sdx = tokend + 1
token = sequence{"terminal", string(src[tokstart+1 : tokend])}
isSeq = true
return
}
}
token = invalid("no closing quote")
isSeq = false
} else if ch >= 'a' && ch <= 'z' {
// To simplify things for the purposes of this task,
// identifiers are strictly a-z only, not A-Z or 1-9.
for {
sdx++
if sdx >= len(src) {
break
}
ch = src[sdx]
if ch < 'a' || ch > 'z' {
break
}
}
token = sequence{"ident", string(src[tokstart:sdx])}
isSeq = true
} else {
token = invalid("invalid ebnf")
isSeq = false
}
}
func matchToken(ch rune) {
if token != ch {
token = invalid(fmt.Sprintf("invalid ebnf (%c expected)", ch))
isSeq = false
} else {
getToken()
}
}
func addIdent(ident string) int {
k := -1
for i, id := range idents {
if id == ident {
k = i
break
}
}
if k == -1 {
idents = append(idents, ident)
k = len(idents) - 1
ididx = append(ididx, -1)
}
return k
}
func factor() object {
var res object
if isSeq {
t := token.([]object)
if t[0] == "ident" {
idx := addIdent(t[1].(string))
t = append(t, idx)
token = t
}
res = token
getToken()
} else if token == '[' {
getToken()
res = sequence{"optional", expression()}
matchToken(']')
} else if token == '(' {
getToken()
res = expression()
matchToken(')')
} else if token == '{' {
getToken()
res = sequence{"repeat", expression()}
matchToken('}')
} else {
panic("invalid token in factor() function")
}
if s, ok := res.(sequence); ok && len(s) == 1 {
return s[0]
}
return res
}
func term() object {
res := sequence{factor()}
tokens := []object{-1, '|', '.', ';', ')', ']', '}'}
outer:
for {
for _, t := range tokens {
if t == token {
break outer
}
}
res = append(res, factor())
}
if len(res) == 1 {
return res[0]
}
return res
}
func expression() object {
res := sequence{term()}
if token == '|' {
res = sequence{"or", res[0]}
for token == '|' {
getToken()
res = append(res, term())
}
}
if len(res) == 1 {
return res[0]
}
return res
}
func production() object {
// Returns a token or -1; the real result is left in 'productions' etc,
getToken()
if token != '}' {
if token == -1 {
return invalid("invalid ebnf (missing closing })")
}
if !isSeq {
return -1
}
t := token.(sequence)
if t[0] != "ident" {
return -1
}
ident := t[1].(string)
idx := addIdent(ident)
getToken()
matchToken('=')
if token == -1 {
return -1
}
productions = append(productions, sequence{ident, idx, expression()})
ididx[idx] = len(productions) - 1
}
return token
}
func parse(ebnf string) int {
// Returns +1 if ok, -1 if bad.
fmt.Printf("parse:\n%s ===>\n", ebnf)
err = false
src = []rune(ebnf)
sdx = 0
idents = idents[:0]
ididx = ididx[:0]
productions = productions[:0]
extras = extras[:0]
getToken()
if isSeq {
t := token.(sequence)
t[0] = "title"
extras = append(extras, token)
getToken()
}
if token != '{' {
return invalid("invalid ebnf (missing opening {)")
}
for {
token = production()
if token == '}' || token == -1 {
break
}
}
getToken()
if isSeq {
t := token.(sequence)
t[0] = "comment"
extras = append(extras, token)
getToken()
}
if token != -1 {
return invalid("invalid ebnf (missing eof?)")
}
if err {
return -1
}
k := -1
for i, idx := range ididx {
if idx == -1 {
k = i
break
}
}
if k != -1 {
return invalid(fmt.Sprintf("invalid ebnf (undefined:%s)", idents[k]))
}
pprint(productions, "productions")
pprint(idents, "idents")
pprint(ididx, "ididx")
pprint(extras, "extras")
return 1
}
// Adjusts Go's normal printing of slices to look more like Phix output.
func pprint(ob object, header string) {
fmt.Printf("\n%s:\n", header)
pp := fmt.Sprintf("%q", ob)
pp = strings.Replace(pp, "[", "{", -1)
pp = strings.Replace(pp, "]", "}", -1)
pp = strings.Replace(pp, " ", ", ", -1)
for i := 0; i < len(idents); i++ {
xs := fmt.Sprintf(`'\x%02d'`, i)
is := fmt.Sprintf("%d", i)
pp = strings.Replace(pp, xs, is, -1)
}
fmt.Println(pp)
}
// The rules that applies() has to deal with are:
// {factors} - if rule[0] is not string,
// just apply one after the other recursively.
// {"terminal", "a1"} -- literal constants
// {"or", <e1>, <e2>, ...} -- (any) one of n
// {"repeat", <e1>} -- as per "{}" in ebnf
// {"optional", <e1>} -- as per "[]" in ebnf
// {"ident", <name>, idx} -- apply the sub-rule
func applies(rule sequence) bool {
wasSdx := sdx // in case of failure
r1 := rule[0]
if _, ok := r1.(string); !ok {
for i := 0; i < len(rule); i++ {
if !applies(rule[i].(sequence)) {
sdx = wasSdx
return false
}
}
} else if r1 == "terminal" {
skipSpaces()
r2 := []rune(rule[1].(string))
for i := 0; i < len(r2); i++ {
if sdx >= len(src) || src[sdx] != r2[i] {
sdx = wasSdx
return false
}
sdx++
}
} else if r1 == "or" {
for i := 1; i < len(rule); i++ {
if applies(rule[i].(sequence)) {
return true
}
}
sdx = wasSdx
return false
} else if r1 == "repeat" {
for applies(rule[1].(sequence)) {
}
} else if r1 == "optional" {
applies(rule[1].(sequence))
} else if r1 == "ident" {
i := rule[2].(int)
ii := ididx[i]
if !applies(productions[ii][2].(sequence)) {
sdx = wasSdx
return false
}
} else {
panic("invalid rule in applies() function")
}
return true
}
func checkValid(test string) {
src = []rune(test)
sdx = 0
res := applies(productions[0][2].(sequence))
skipSpaces()
if sdx < len(src) {
res = false
}
fmt.Printf("%q, %s\n", test, results[1-btoi(res)])
}
func main() {
ebnfs := []string{
`"a" {
a = "a1" ( "a2" | "a3" ) { "a4" } [ "a5" ] "a6" ;
} "z" `,
`{
expr = term { plus term } .
term = factor { times factor } .
factor = number | '(' expr ')' .
plus = "+" | "-" .
times = "*" | "/" .
number = digit { digit } .
digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" .
}`,
`a = "1"`,
`{ a = "1" ;`,
`{ hello world = "1"; }`,
`{ foo = bar . }`,
}
tests := [][]string{
{
"a1a3a4a4a5a6",
"a1 a2a6",
"a1 a3 a4 a6",
"a1 a4 a5 a6",
"a1 a2 a4 a5 a5 a6",
"a1 a2 a4 a5 a6 a7",
"your ad here",
},
{
"2",
"2*3 + 4/23 - 7",
"(3 + 4) * 6-2+(4*(4))",
"-2",
"3 +",
"(4 + 3",
},
}
for i, ebnf := range ebnfs {
if parse(ebnf) == +1 {
fmt.Println("\ntests:")
for _, test := range tests[i] {
checkValid(test)
}
}
fmt.Println()
}
}</syntaxhighlight>
{{out}}
<pre>
parse:
"a" {
a = "a1" ( "a2" | "a3" ) { "a4" } [ "a5" ] "a6" ;
} "z" ===>
productions:
{{"a", 0, {{"terminal", "a1"}, {"or", {"terminal", "a2"}, {"terminal", "a3"}}, {"repeat", {"terminal", "a4"}}, {"optional", {"terminal", "a5"}}, {"terminal", "a6"}}}}
idents:
{"a"}
ididx:
{0}
extras:
{{"title", "a"}, {"comment", "z"}}
tests:
"a1a3a4a4a5a6", pass
"a1 a2a6", pass
"a1 a3 a4 a6", pass
"a1 a4 a5 a6", fail
"a1 a2 a4 a5 a5 a6", fail
"a1 a2 a4 a5 a6 a7", fail
"your ad here", fail
parse:
{
expr = term { plus term } .
term = factor { times factor } .
factor = number | '(' expr ')' .
plus = "+" | "-" .
times = "*" | "/" .
number = digit { digit } .
digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" .
} ===>
productions:
{{"expr", 0, {{"ident", "term", 1}, {"repeat", {{"ident", "plus", 2}, {"ident", "term", 1}}}}}, {"term", 1, {{"ident", "factor", 3}, {"repeat", {{"ident", "times", 4}, {"ident", "factor", 3}}}}}, {"factor", 3, {"or", {"ident", "number", 5}, {{"terminal", "("}, {"ident", "expr", 0}, {"terminal", ")"}}}}, {"plus", 2, {"or", {"terminal", "+"}, {"terminal", "-"}}}, {"times", 4, {"or", {"terminal", "*"}, {"terminal", "/"}}}, {"number", 5, {{"ident", "digit", 6}, {"repeat", {"ident", "digit", 6}}}}, {"digit", 6, {"or", {"terminal", "0"}, {"terminal", "1"}, {"terminal", "2"}, {"terminal", "3"}, {"terminal", "4"}, {"terminal", "5"}, {"terminal", "6"}, {"terminal", "7"}, {"terminal", "8"}, {"terminal", "9"}}}}
idents:
{"expr", "term", "plus", "factor", "times", "number", "digit"}
ididx:
{0, 1, 3, 2, 4, 5, 6}
extras:
{}
tests:
"2", pass
"2*3 + 4/23 - 7", pass
"(3 + 4) * 6-2+(4*(4))", pass
"-2", fail
"3 +", fail
"(4 + 3", fail
parse:
a = "1" ===>
invalid ebnf (missing opening {)
parse:
{ a = "1" ; ===>
invalid ebnf (missing closing })
parse:
{ hello world = "1"; } ===>
invalid ebnf (= expected)
parse:
{ foo = bar . } ===>
invalid ebnf (undefined:bar)
</pre>
=={{header|Haskell}}==
We use Parsec to generate Parsec.
<syntaxhighlight lang="haskell">import Control.Applicative
import Control.Monad
import Data.Maybe
import qualified Data.Map as M
import System.Environment (getArgs)
import Text.Parsec hiding (many, optional, (<|>))
import Text.Parsec.String
import Text.Parsec.Error
-----------------------------------------------------------------
-- Main
-----------------------------------------------------------------
main = do
{- Uses the EBNF grammar contained in the first file to parse
the second file, then prints a parse tree. -}
[grammar_file, other_file] <- getArgs
ebnf_text <- readFile grammar_file
case parseGrammar grammar_file ebnf_text of
Left err ->
putStrLn $ "Failed to parse EBNF grammar: " ++ show err
Right g -> do
putStrLn "Successfully parsed EBNF grammar."
o <- readFile other_file
case parseWithGrammar g other_file o of
Left err ->
putStrLn $ "Failed to parse second file: " ++ show err
Right tree ->
print tree
-----------------------------------------------------------------
-- Types and user functions
-----------------------------------------------------------------
parseGrammar :: FilePath -> String -> Either ParseError Grammar
parseGrammar fp s =
case runParser ebnf M.empty fp s of
Left e ->
Left e
Right (Grammar g, usedNames) ->
let undefinedRules = foldl (flip M.delete) usedNames $ map fst g
(undefName, undefNamePos) = M.findMin undefinedRules
in if M.null undefinedRules
then Right $ Grammar g
else Left $ newErrorMessage
(Message $ "Undefined rule: " ++ undefName)
undefNamePos
parseWithGrammar :: Grammar -> FilePath -> String -> Either ParseError ParseTree
parseWithGrammar g@(Grammar ((_, firstR) : _)) fp s =
runParser (liftA cleanTree $ firstR <* eof) g fp s
type GParser = Parsec String UsedNames
type UsedNames = M.Map String SourcePos
type Rule = Parsec String Grammar ParseTree
-- We need to keep the Grammar around as a Parsec user state
-- to look up named rules.
data Grammar = Grammar [(String, Rule)]
-- Grammar would be a type synonym instead of an ADT, but
-- infinite types aren't allowed in Haskell.
data ParseTree =
ParseBranch String [ParseTree] |
ParseLeaf String
instance Show ParseTree where
show = showIndented 0
-- show (ParseBranch "" t) = '[' : concatMap ((' ' :) . show) t ++ "]"
-- show (ParseBranch s t) = '(' : s ++ concatMap ((' ' :) . show) t ++ ")"
-- show (ParseLeaf s) = show s
showIndented :: Int -> ParseTree -> String
showIndented i (ParseBranch "" []) =
indent i "[]"
showIndented i (ParseBranch "" t) =
indent i "[" ++
concatMap (showIndented (i + 2)) t ++
"]"
showIndented i (ParseBranch s t) =
indent i ("(" ++ s) ++
concatMap (showIndented (i + 2)) t ++
")"
showIndented i (ParseLeaf s) =
indent i $ show s
indent :: Int -> String -> String
indent i s = "\n" ++ replicate i ' ' ++ s
cleanTree :: ParseTree -> ParseTree
-- Removes empty anonymous branches.
cleanTree (ParseBranch i ts) =
ParseBranch i $ map cleanTree $ filter p ts
where p (ParseBranch "" []) = False
p _ = True
cleanTree x = x
-----------------------------------------------------------------
-- GParser definitions
-----------------------------------------------------------------
ebnf :: GParser (Grammar, UsedNames)
ebnf = liftA2 (,) (ws *> syntax <* eof) getState
syntax :: GParser Grammar
syntax = liftA Grammar $
optional title *>
lcbtw '{' '}' (many production) <*
optional comment
production :: GParser (String, Rule)
production = do
i <- identifier
lc '='
r <- expression
oneOf ".;"
ws
return (i, liftM (nameBranch i) r)
where nameBranch i (ParseBranch _ l) = ParseBranch i l
expression, term :: GParser Rule
expression = liftA (foldl1 (<|>)) $ term `sepBy1` (lc '|')
term = liftA (branch . sequence) $ many1 factor
factor :: GParser Rule
factor = liftA try $
liftA ruleByName rememberName <|>
liftA (leaf . (<* ws) . string) literal <|>
liftA perhaps (lcbtw '[' ']' expression) <|>
lcbtw '(' ')' expression <|>
liftA (branch . many) (lcbtw '{' '}' expression)
where rememberName :: GParser String
rememberName = do
i <- identifier
p <- getPosition
modifyState $ M.insertWith (flip const) i p
{- Adds i → p to the state only if i doesn't
already have an entry. This ensures we report the
*first* usage of each unknown identifier. -}
return i
ruleByName :: String -> Rule
ruleByName name = do
Grammar g <- getState
fromJust (lookup name g) <?> name
perhaps = option $ ParseLeaf ""
identifier :: GParser String
identifier = many1 (noneOf " \t\n=|(){}[].;\"'") <* ws
title = literal
comment = literal
literal =
(lc '\'' *> manyTill anyChar (lc '\'')) <|>
(lc '"' *> manyTill anyChar (lc '"'))
<* ws
-----------------------------------------------------------------
-- Miscellany
-----------------------------------------------------------------
leaf = liftA ParseLeaf
branch = liftA $ ParseBranch ""
lcbtw c1 c2 = between (lc c1) (lc c2)
lc :: Char -> GParser Char
lc c = char c <* ws
ws = many $ oneOf " \n\t"</syntaxhighlight>
=={{header|Julia}}==
Creates a Grammar struct from an EBNF grammar, which has a matching Regex for each production of the EBNF grammar.
Tested with Julia v1.7.2
<syntaxhighlight lang="julia">
struct Grammar
regex::Regex
rules::Dict{Symbol,Regex}
root::Regex
function Grammar(regex::Regex)
names = keys(match(regex, ""))
new(regex,
Dict{Symbol,Regex}(
Symbol(name) => Regex(
"$(regex.pattern)(?&$(name))",
regex.compile_options,
regex.match_options
)
for name in names if name isa String),
Regex(
"$(regex.pattern)^\\s*(?&$(first(names)))\\s*\$",
regex.compile_options,
regex.match_options))
end
end
Base.getindex(grammar::Grammar, key) = grammar.rules[key]
Base.occursin(grammar::Grammar, str::AbstractString) = occursin(grammar.root, str)
Base.show(io::IO, grammar::Grammar) = print(io, "Grammar(", grammar.regex, ")")
const ebnfgrammar = Grammar(r"""
(?(DEFINE) # EBNF syntax
(?<syntax>
(?&title)? \s*+ { \s*+ ( (?&production) \s*+ )* } \s*+ (?&comment)? )
(?<production>
(?&identifier) \s*+ = \s*+ (?&expression) \s*+ [.;] )
(?<expression>
(?&term) ( \s*+ \| \s*+ (?&term) )* )
(?<term>
(?&factor) ( \s*+ (?&factor) )* )
(?<factor>
(?&identifier)
| (?&literal)
| \[ \s*+ (?&expression) \s*+ \]
| \( \s*+ (?&expression) \s*+ \)
| { \s*+ (?&expression) \s*+ } )
(?<identifier>
[^'"\s=|(){}[\].;]+ )
(?<title>
(?&literal) )
(?<comment>
(?&literal) )
(?<literal>
' [^']+ '
| " [^"]+ " )
)"""x)
function syntax(grammar::Grammar, str::AbstractString)
if occursin(grammar[:syntax], str)
"""(?(DEFINE)$(join(production(grammar, eachmatch(grammar[:production], str)))))"""
else
throw(ErrorException("Invalid EBNF syntax."))
end
end
production(grammar::Grammar, iter) = (production(grammar, m.match) for m in iter)
function production(grammar::Grammar, str::AbstractString)
rstrip(c -> isspace(c) || c == '.' || c == ';', str)
id, expr = split(str, r"\s*=\s*", limit=2)
"(?<$(id)>" * join(
expression(grammar, eachmatch(grammar[:expression], expr)),
"\\s*+|\\s*+") * "\\s*+)"
end
expression(grammar::Grammar, iter) = (expression(grammar, m.match) for m in iter)
function expression(grammar::Grammar, str::AbstractString)
join(term(grammar, eachmatch(grammar[:term], str)), "\\s*+|\\s*+")
end
term(grammar::Grammar, iter) = (term(grammar, m.match) for m in iter)
function term(grammar::Grammar, str::AbstractString)
join(factor(grammar, eachmatch(grammar[:factor], str)), "\\s*+")
end
factor(grammar::Grammar, iter) = (factor(grammar, m.match) for m in iter)
function factor(grammar::Grammar, str::AbstractString)
str = strip(str)
if startswith(str, r"['\"]")
literal(grammar, str)
elseif startswith(str, r"[[({]")
"(\\s*+" * expression(grammar, str[begin+1:end-1]) * (
if startswith(str, '[')
"\\s*+)?"
elseif startswith(str, '{')
"\\s*+)*"
else
"\\s*+)"
end
)
else
"(?&$(str))"
end
end
literal(::Grammar, str::AbstractString) = "\\Q$(str[begin+1:end-1])\\E"
grammar(ebnf::AbstractString) = Grammar(Regex(syntax(ebnfgrammar, ebnf)))
using Test
oneliner = grammar("""
"a" {
a = "a1" ( "a2" | "a3" ) { "a4" } [ "a5" ] "a6" ;
} "z"
""")
@testset "One liner" begin
@test occursin(oneliner, "a1a3a4a4a5a6")
@test occursin(oneliner, "a1 a2a6")
@test occursin(oneliner, "a1 a3 a4 a6")
@test !occursin(oneliner, "a1 a4 a5 a6")
@test !occursin(oneliner, "a1 a2 a4 a5 a5 a6")
@test !occursin(oneliner, "a1 a2 a4 a5 a6 a7")
@test !occursin(oneliner, "your ad here")
end
arithmetic = grammar("""
{
expr = term { plus term } .
term = factor { times factor } .
factor = number | '(' expr ')' .
plus = "+" | "-" .
times = "*" | "/" .
number = digit { digit } .
digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" .
}
""")
@testset "Arithmetic expressions" begin
@test occursin(arithmetic, "2")
@test occursin(arithmetic, "2*3 + 4/23 - 7")
@test occursin(arithmetic, "(3 + 4) * 6-2+(4*(4))")
@test !occursin(arithmetic, "-2")
@test !occursin(arithmetic, "3 +")
@test !occursin(arithmetic, "(4 + 3")
end
@testset "Invalid EBNF" begin
@test_throws ErrorException grammar("""a = "1";""")
@test_throws ErrorException grammar("""{ a = "1";""")
@test_throws ErrorException grammar("""{ hello world = "1"; }""")
@test_throws ErrorException grammar("{ foo = bar . }")
end
</syntaxhighlight>
=={{header|Modula-2}}==
<syntaxhighlight lang="modula2">MODULE EBNF;
FROM ASCII IMPORT EOL;
FROM InOut IMPORT Done, Read, Write, WriteLn, WriteInt, WriteString;
FROM EBNFScanner IMPORT Symbol, sym, id, Ino, GetSym, MarkError, SkipLine;
FROM TableHandler IMPORT WordLength, Table, overflow, InitTable, Record, Tabulate;
VAR T0, T1 : Table;
PROCEDURE skip (n : INTEGER);
BEGIN
MarkError (n);
WHILE (sym < lpar) OR (sym > period) DO GetSym END
END skip;
PROCEDURE Expression;
PROCEDURE Term;
PROCEDURE Factor;
BEGIN
IF sym = ident THEN
Record (T0, id, Ino);
GetSym
ELSIF sym = literal THEN
Record (T1, id, Ino);
GetSym
ELSIF sym = lpar THEN
GetSym;
Expression;
IF sym = rpar THEN GetSym ELSE skip (2) END
ELSIF sym = lbk THEN
GetSym;
Expression;
IF sym = rbk THEN GetSym ELSE skip (3) END
ELSIF sym = lbr THEN
GetSym;
Expression;
IF sym = rbr THEN GetSym ELSE skip (4) END
ELSE
skip (5)
END
END Factor;
BEGIN
Factor;
WHILE sym < bar DO Factor END
END Term;
BEGIN
Term;
WHILE sym = bar DO
GetSym;
Term
END
END Expression;
PROCEDURE Production;
BEGIN
Record (T0, id, - INTEGER (Ino));
GetSym;
IF sym = eql THEN GetSym ELSE skip (7) END;
Expression;
IF sym # period THEN
MarkError (8);
SkipLine
END;
GetSym
END Production;
BEGIN
InitTable (T0);
InitTable (T1);
GetSym;
WHILE (sym = ident) AND (overflow = 0) DO Production END;
IF overflow > 0 THEN
WriteLn;
WriteString ("Table overflow");
WriteInt (overflow, 6);
END;
Write (35C);
Tabulate (T0);
Tabulate (T1);
END EBNF.</syntaxhighlight>
And the source for the EBNF scanner. I hope you like nested procedures.
<syntaxhighlight lang="modula2">IMPLEMENTATION MODULE EBNFScanner;
FROM ASCII IMPORT LF;
FROM InOut IMPORT Read, Write, WriteLn, WriteInt, WriteBf, EOF;
VAR ch : CHAR;
MODULE LineHandler;
IMPORT LF, EOF, ch, Ino, Read, Write, WriteLn, WriteInt, WriteBf;
EXPORT GetCh, MarkError, SkipLine;
CONST LineWidth = 100;
VAR cc : INTEGER;
cc1 : INTEGER;
cc2 : INTEGER;
line : ARRAY [0..LineWidth - 1] OF CHAR;
PROCEDURE GetLine;
BEGIN
IF cc2 > 0 THEN
WriteLn;
cc2 := 0
END;
Read (ch);
IF EOF () THEN
line [0] := 177C;
cc1 := 1
ELSE
INC (Ino);
WriteInt (Ino, 5);
Write (' ');
cc1 := 0;
LOOP
Write (ch);
line [cc1] := ch;
INC (cc1);
IF ch = LF THEN EXIT END;
Read (ch)
END
END
END GetLine;
PROCEDURE GetCh;
BEGIN
WHILE cc = cc1 DO
cc := 0;
GetLine
END;
ch := line [cc];
INC (cc)
END GetCh;
PROCEDURE MarkError (n : INTEGER);
BEGIN
IF cc2 = 0 THEN
Write ('*');
cc2 := 3;
REPEAT
Write (' ');
DEC (cc2)
UNTIL cc2 = 0;
END;
WHILE cc2 < cc DO
Write (' ');
INC (cc2)
END;
Write ('^');
WriteInt (n, 1);
INC (cc2, 2)
END MarkError;
PROCEDURE SkipLine;
BEGIN
WHILE ch # LF DO GetCh END;
GetCh
END SkipLine;
BEGIN (* BEGIN of LineHandler *)
cc := 0;
cc1 := 0;
cc2 := 0
END LineHandler;
PROCEDURE GetSym;
VAR i : CARDINAL;
BEGIN
WHILE ch <= ' ' DO GetCh END;
IF ch = '/' THEN
SkipLine;
WHILE ch <= ' ' DO GetCh END
END;
IF (CAP (ch) <= 'Z') AND (CAP (ch) >= 'A') THEN
i := 0;
sym := literal;
REPEAT
IF i < IdLength THEN
id [i] := ch;
INC (i)
END;
IF ch > 'Z' THEN sym := ident END;
GetCh
UNTIL (CAP (ch) < 'A') OR (CAP (ch) > 'Z');
id [i] := ' '
ELSIF ch = "'" THEN
i := 0;
GetCh;
sym := literal;
WHILE ch # "'" DO
IF i < IdLength THEN
id [i] := ch;
INC (i)
END;
GetCh
END;
GetCh;
id [i] := ' '
WHILE ch # "'" DO
IF i < IdLength THEN
id [i] := ch;
INC (i)
END;
GetCh
END;
GetCh;
id [i] := ' '
ELSIF ch = '"' THEN
i := 0;
GetCh;
sym := literal;
WHILE ch # '"' DO
IF i < IdLength THEN
id [i] := ch;
INC (i)
END;
GetCh
END;
GetCh;
id [i] := ' '
ELSIF ch = '=' THEN sym := eql; GetCh
ELSIF ch = '(' THEN sym := lpar; GetCh
ELSIF ch = ')' THEN sym := rpar; GetCh
ELSIF ch = '[' THEN sym := lbk; GetCh
ELSIF ch = ']' THEN sym := rbk; GetCh
ELSIF ch = '{' THEN sym := lbr; GetCh
ELSIF ch = '}' THEN sym := rbr; GetCh
ELSIF ch = '|' THEN sym := bar; GetCh
ELSIF ch = '.' THEN sym := period; GetCh
ELSIF ch = 177C THEN sym := other; GetCh
ELSE
sym := other;
GetCh
END
END GetSym;
BEGIN
Ino := 0;
ch := ' '
END EBNFScanner.</syntaxhighlight>
=={{header|Perl}}==
<syntaxhighlight lang="perl">#!/usr/bin/perl
use strict; # http://www.rosettacode.org/wiki/Parse_EBNF
use warnings;
$SIG{__WARN__} = sub { print "\nWARN: @_\n"; exit };
my $h = qr/\G\s*/;
my $identifier = qr/$h([a-z]\w*)\b/i;
my $literal = qr/$h(['"])(.+?)\1/s;
my ($title, $comment, %productions, %called, $startsymbol, $show, $errpos);
sub node { bless [ @_[1..$#_] ], $_[0] }
sub err { die "ERROR: ", s/\G\s*\K/<**ERROR @_**>/r, "\n" }
sub want { /$h\Q$_[1]\E/gc ? shift : err "missing '$_[1]' " }
sub addin { node $_[0] => ref $_[1] eq $_[0] ? @{$_[1]} : $_[1], pop }
for my $case ( split /^-{50}.*\n/m, do { local $/; @ARGV ? <> : <DATA> } )
{
$show = $case =~ s/^#show.*//m;
my ($ebnf, $tests) = map s/^#.*\n//gmr, split /^#test.*\n/m, $case, 2;
parse( $ebnf, ($tests // "") =~ /.*\n/g );
}
sub parse
{
eval
{
(%productions, %called, $startsymbol) = ();
local $_ = shift // 'empty ebnf source string';
print '-' x 75, "\n", s/\s*\z/\n\n/r;
syntax(); ################################################## parse the EBNF
print " title: $title\n comment: $comment\n";
$startsymbol or err "no productions";
print "start symbol: $startsymbol\n";
for my $key ( sort keys %productions )
{
$show and print "\n$key =\n", $productions{$key}->show =~ s/^/ /gmr;
}
delete @called{keys %productions};
%called and die "\nERROR: undefined production(s) <@{[ keys %called]}>\n";
for ( @_ ) ###################################################### run tests
{
$errpos = undef;
print "\ntry: $_";
print eval
{
$productions{$startsymbol}->run or pos($_) = $errpos, err; ### run tree
/$h\n/gc or err 'incomplete parse';
} ? "valid\n" : $@;
}
1;
} or print "$@\n";
}
sub syntax ############################################## subs for parsing EBNF
{
$title = /$literal/gc ? $2 : 'none';
/$h\{/gc or err 'missing open brace';
while( /$identifier\s*=/gc ) # is this the start of a production
{
my $name = $1;
$startsymbol //= $name;
my $tree = expr(0);
$productions{$name} =
$productions{$name} ? addin ALT => $productions{$name}, $tree : $tree;
/$h[.;]/gc or err 'missing production terminator';
}
/$h\}/gc or err 'missing close brace';
$comment = /$literal/gc ? $2 : 'none';
/$h\z/gc or err 'extra characters after parse';
}
sub expr
{
my $tree =
/$identifier/gc ? do { $called{$1}++; node PROD => $1 } :
/$literal/gc ? node LIT => $2 :
/$h\[/gc ? node OPTION => want expr(0), ']' :
/$h\{/gc ? node REPEAT => want expr(0), '}' :
/$h\(/gc ? want expr(0), ')' :
err 'Invalid expression';
$tree =
/\G\s+/gc ? $tree :
$_[0] <= 1 && /\G(?=[[{('"a-z])/gci ? addin SEQ => $tree, expr(2) :
$_[0] <= 0 && /\G\|/gc ? addin ALT => $tree, expr(1) :
return $tree while 1;
}
################################################### run parse tree
sub LIT::run { /$h\Q$_[0][0]\E/gc }
sub SEQ::run
{
my $pos = pos($_) // 0;
for my $node ( @{ $_[0] } )
{
$node->run or $errpos = pos($_), pos($_) = $pos, return 0;
}
return 1;
}
sub OPTION::run
{
my $pos = pos($_) // 0;
$_[0][0]->run or pos($_) = $pos, return 1;
}
sub PROD::run
{
$productions{ $_[0][0] }->run;
}
sub REPEAT::run
{
my $pos = pos($_) // 0;
$pos = pos($_) while $_[0][0]->run;
pos($_) = $pos;
return 1;
}
sub ALT::run
{
my $pos = pos($_) // 0;
for my $node ( @{ $_[0] } )
{
eval{ $node->run } and return 1;
pos($_) = $pos;
}
return 0;
}
sub LIT::show { "LIT $_[0][0]\n" } ###################### for nested tree print
sub PROD::show { "PROD $_[0][0]\n" }
sub UNIVERSAL::show
{
join '', ref $_[0], "\n", map $_->show =~ s/^/ /gmr, @{ $_[0] };
}
__DATA__
"a" {
a = "a1" ( "a2" | "a3" ) { "a4" } [ "a5" ] "a6" ;
} "z"
#show
#tests
a1a3a4a4a5a6
a1 a2a6
a1 a3 a4 a6
a1 a4 a5 a6
a1 a2 a4 a5 a5 a6
a1 a2 a4 a5 a6 a7
your ad here
----------------------------------------------------------------------
"Arithmetic expressions" {
expr = term { plus term } .
term = factor { times factor } .
factor = number | '(' expr ')' .
plus = "+" | "-" .
times = "*" | "/" .
number = digit { digit } .
digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" .
} 'http://www.rosettacode.org/wiki/Parse_EBNF'
#tests
2
2*3 + 4/23 - 7
(3 + 4) * 6-2+(4*(4))
-2
3 +
(4 + 3
----------------------------------------------------------------------
'some invalid EBNF' { a = "1" ;
----------------------------------------------------------------------
a = "1";
----------------------------------------------------------------------
{ hello world = "1"; }
----------------------------------------------------------------------
{ foo = bar . } "undefined production check"
----------------------------------------------------------------------</syntaxhighlight>
{{out}}
<pre>
---------------------------------------------------------------------------
"a" {
a = "a1" ( "a2" | "a3" ) { "a4" } [ "a5" ] "a6" ;
} "z"
title: a
comment: z
start symbol: a
a =
SEQ
LIT a1
ALT
LIT a2
LIT a3
REPEAT
LIT a4
OPTION
LIT a5
LIT a6
try: a1a3a4a4a5a6
valid
try: a1 a2a6
valid
try: a1 a3 a4 a6
valid
try: a1 a4 a5 a6
ERROR: a1 <**ERROR **>a4 a5 a6
try: a1 a2 a4 a5 a5 a6
ERROR: a1 a2 a4 a5 <**ERROR **>a5 a6
try: a1 a2 a4 a5 a6 a7
ERROR: a1 a2 a4 a5 a6 <**ERROR incomplete parse**>a7
try: your ad here
ERROR: <**ERROR **>your ad here
---------------------------------------------------------------------------
"Arithmetic expressions" {
expr = term { plus term } .
term = factor { times factor } .
factor = number | '(' expr ')' .
plus = "+" | "-" .
times = "*" | "/" .
number = digit { digit } .
digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" .
} 'http://www.rosettacode.org/wiki/Parse_EBNF'
title: Arithmetic expressions
comment: http://www.rosettacode.org/wiki/Parse_EBNF
start symbol: expr
try: 2
valid
try: 2*3 + 4/23 - 7
valid
try: (3 + 4) * 6-2+(4*(4))
valid
try: -2
ERROR: <**ERROR **>-2
try: 3 +
ERROR: 3 <**ERROR incomplete parse**>+
try: (4 + 3
ERROR: <**ERROR **>(4 + 3
---------------------------------------------------------------------------
'some invalid EBNF' { a = "1" ;
ERROR: 'some invalid EBNF' { a = "1" ;
<**ERROR missing close brace**>
---------------------------------------------------------------------------
a = "1";
ERROR: <**ERROR missing open brace**>a = "1";
---------------------------------------------------------------------------
{ hello world = "1"; }
ERROR: { <**ERROR missing close brace**>hello world = "1"; }
---------------------------------------------------------------------------
{ foo = bar . } "undefined production check"
title: none
comment: undefined production check
start symbol: foo
ERROR: undefined production(s) <bar>
</pre>
=={{header|Phix}}==
<!--<syntaxhighlight lang="phix">(phixonline)-->
<span style="color: #008080;">with</span> <span style="color: #008080;">javascript_semantics</span>
<span style="color: #004080;">string</span> <span style="color: #000000;">src</span>
<span style="color: #004080;">integer</span> <span style="color: #000000;">ch</span><span style="color: #0000FF;">,</span> <span style="color: #000000;">sdx</span>
<span style="color: #004080;">object</span> <span style="color: #000000;">token</span>
<span style="color: #004080;">bool</span> <span style="color: #000000;">error</span> <span style="color: #0000FF;">=</span> <span style="color: #004600;">false</span>
<span style="color: #008080;">function</span> <span style="color: #000000;">invalid</span><span style="color: #0000FF;">(</span><span style="color: #004080;">string</span> <span style="color: #000000;">msg</span><span style="color: #0000FF;">)</span>
<span style="color: #000000;">error</span> <span style="color: #0000FF;">=</span> <span style="color: #004600;">true</span>
<span style="color: #0000FF;">?</span><span style="color: #000000;">msg</span>
<span style="color: #000000;">sdx</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">length</span><span style="color: #0000FF;">(</span><span style="color: #000000;">src</span><span style="color: #0000FF;">)+</span><span style="color: #000000;">1</span> <span style="color: #000080;font-style:italic;">-- (set to eof)</span>
<span style="color: #008080;">return</span> <span style="color: #0000FF;">-</span><span style="color: #000000;">1</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">function</span>
<span style="color: #008080;">procedure</span> <span style="color: #000000;">skip_spaces</span><span style="color: #0000FF;">()</span>
<span style="color: #008080;">while</span> <span style="color: #000000;">1</span> <span style="color: #008080;">do</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">sdx</span><span style="color: #0000FF;">></span><span style="color: #7060A8;">length</span><span style="color: #0000FF;">(</span><span style="color: #000000;">src</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">then</span> <span style="color: #008080;">exit</span> <span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #000000;">ch</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">src</span><span style="color: #0000FF;">[</span><span style="color: #000000;">sdx</span><span style="color: #0000FF;">]</span>
<span style="color: #008080;">if</span> <span style="color: #008080;">not</span> <span style="color: #7060A8;">find</span><span style="color: #0000FF;">(</span><span style="color: #000000;">ch</span><span style="color: #0000FF;">,{</span><span style="color: #008000;">' '</span><span style="color: #0000FF;">,</span><span style="color: #008000;">'\t'</span><span style="color: #0000FF;">,</span><span style="color: #008000;">'\r'</span><span style="color: #0000FF;">,</span><span style="color: #008000;">'\n'</span><span style="color: #0000FF;">})</span> <span style="color: #008080;">then</span> <span style="color: #008080;">exit</span> <span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #000000;">sdx</span> <span style="color: #0000FF;">+=</span> <span style="color: #000000;">1</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">while</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">procedure</span>
<span style="color: #008080;">procedure</span> <span style="color: #000000;">get_token</span><span style="color: #0000FF;">()</span>
<span style="color: #000080;font-style:italic;">-- yeilds a single character token, one of {}()[]|=.;
-- or {"terminal",string} or {"ident", string} or -1.</span>
<span style="color: #000000;">skip_spaces</span><span style="color: #0000FF;">()</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">sdx</span><span style="color: #0000FF;">></span><span style="color: #7060A8;">length</span><span style="color: #0000FF;">(</span><span style="color: #000000;">src</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">then</span>
<span style="color: #000000;">token</span> <span style="color: #0000FF;">=</span> <span style="color: #0000FF;">-</span><span style="color: #000000;">1</span>
<span style="color: #008080;">return</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #004080;">integer</span> <span style="color: #000000;">tokstart</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">sdx</span>
<span style="color: #008080;">if</span> <span style="color: #7060A8;">find</span><span style="color: #0000FF;">(</span><span style="color: #000000;">ch</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"{}()[]|=.;"</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">then</span>
<span style="color: #000000;">sdx</span> <span style="color: #0000FF;">+=</span> <span style="color: #000000;">1</span>
<span style="color: #000000;">token</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">ch</span>
<span style="color: #008080;">elsif</span> <span style="color: #000000;">ch</span><span style="color: #0000FF;">=</span><span style="color: #008000;">'\"'</span>
<span style="color: #008080;">or</span> <span style="color: #000000;">ch</span><span style="color: #0000FF;">=</span><span style="color: #008000;"><nowiki>'\''</nowiki></span> <span style="color: #008080;">then</span>
<span style="color: #004080;">integer</span> <span style="color: #000000;">closech</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">ch</span>
<span style="color: #008080;">for</span> <span style="color: #000000;">tokend</span><span style="color: #0000FF;">=</span><span style="color: #000000;">sdx</span><span style="color: #0000FF;">+</span><span style="color: #000000;">1</span> <span style="color: #008080;">to</span> <span style="color: #7060A8;">length</span><span style="color: #0000FF;">(</span><span style="color: #000000;">src</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">do</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">src</span><span style="color: #0000FF;">[</span><span style="color: #000000;">tokend</span><span style="color: #0000FF;">]</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">closech</span> <span style="color: #008080;">then</span>
<span style="color: #000000;">sdx</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">tokend</span><span style="color: #0000FF;">+</span><span style="color: #000000;">1</span>
<span style="color: #000000;">token</span> <span style="color: #0000FF;">=</span> <span style="color: #0000FF;">{</span><span style="color: #008000;">"terminal"</span><span style="color: #0000FF;">,</span><span style="color: #000000;">src</span><span style="color: #0000FF;">[</span><span style="color: #000000;">tokstart</span><span style="color: #0000FF;">+</span><span style="color: #000000;">1</span><span style="color: #0000FF;">..</span><span style="color: #000000;">tokend</span><span style="color: #0000FF;">-</span><span style="color: #000000;">1</span><span style="color: #0000FF;">]}</span>
<span style="color: #008080;">return</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">for</span>
<span style="color: #000000;">token</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">invalid</span><span style="color: #0000FF;">(</span><span style="color: #008000;">"no closing quote"</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">elsif</span> <span style="color: #000000;">ch</span><span style="color: #0000FF;">>=</span><span style="color: #008000;">'a'</span> <span style="color: #008080;">and</span> <span style="color: #000000;">ch</span><span style="color: #0000FF;"><=</span><span style="color: #008000;">'z'</span> <span style="color: #008080;">then</span>
<span style="color: #000080;font-style:italic;">-- to simplify things for the purposes of this task,
-- identifiers are strictly a-z only, not A-Z or 1-9</span>
<span style="color: #008080;">while</span> <span style="color: #000000;">1</span> <span style="color: #008080;">do</span>
<span style="color: #000000;">sdx</span> <span style="color: #0000FF;">+=</span> <span style="color: #000000;">1</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">sdx</span><span style="color: #0000FF;">></span><span style="color: #7060A8;">length</span><span style="color: #0000FF;">(</span><span style="color: #000000;">src</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">then</span> <span style="color: #008080;">exit</span> <span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #000000;">ch</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">src</span><span style="color: #0000FF;">[</span><span style="color: #000000;">sdx</span><span style="color: #0000FF;">]</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">ch</span><span style="color: #0000FF;"><</span><span style="color: #008000;">'a'</span> <span style="color: #008080;">or</span> <span style="color: #000000;">ch</span><span style="color: #0000FF;">></span><span style="color: #008000;">'z'</span> <span style="color: #008080;">then</span> <span style="color: #008080;">exit</span> <span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">while</span>
<span style="color: #000000;">token</span> <span style="color: #0000FF;">=</span> <span style="color: #0000FF;">{</span><span style="color: #008000;">"ident"</span><span style="color: #0000FF;">,</span><span style="color: #000000;">src</span><span style="color: #0000FF;">[</span><span style="color: #000000;">tokstart</span><span style="color: #0000FF;">..</span><span style="color: #000000;">sdx</span><span style="color: #0000FF;">-</span><span style="color: #000000;">1</span><span style="color: #0000FF;">]}</span>
<span style="color: #008080;">else</span>
<span style="color: #000000;">token</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">invalid</span><span style="color: #0000FF;">(</span><span style="color: #008000;">"invalid ebnf"</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">procedure</span>
<span style="color: #008080;">procedure</span> <span style="color: #000000;">match_token</span><span style="color: #0000FF;">(</span><span style="color: #004080;">integer</span> <span style="color: #000000;">ch</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">token</span><span style="color: #0000FF;">!=</span><span style="color: #000000;">ch</span> <span style="color: #008080;">then</span>
<span style="color: #000000;">token</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">invalid</span><span style="color: #0000FF;">(</span><span style="color: #7060A8;">sprintf</span><span style="color: #0000FF;">(</span><span style="color: #008000;">"invalid ebnf (%c expected)"</span><span style="color: #0000FF;">,</span><span style="color: #000000;">ch</span><span style="color: #0000FF;">))</span>
<span style="color: #008080;">else</span>
<span style="color: #000000;">get_token</span><span style="color: #0000FF;">()</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">procedure</span>
<span style="color: #004080;">sequence</span> <span style="color: #000000;">idents</span> <span style="color: #0000FF;">=</span> <span style="color: #0000FF;">{},</span>
<span style="color: #000000;">ididx</span> <span style="color: #0000FF;">=</span> <span style="color: #0000FF;">{}</span>
<span style="color: #008080;">function</span> <span style="color: #000000;">add_ident</span><span style="color: #0000FF;">(</span><span style="color: #004080;">string</span> <span style="color: #000000;">ident</span><span style="color: #0000FF;">)</span>
<span style="color: #004080;">integer</span> <span style="color: #000000;">k</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">find</span><span style="color: #0000FF;">(</span><span style="color: #000000;">ident</span><span style="color: #0000FF;">,</span><span style="color: #000000;">idents</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">k</span><span style="color: #0000FF;">=</span><span style="color: #000000;">0</span> <span style="color: #008080;">then</span>
<span style="color: #000000;">idents</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">append</span><span style="color: #0000FF;">(</span><span style="color: #000000;">idents</span><span style="color: #0000FF;">,</span><span style="color: #000000;">ident</span><span style="color: #0000FF;">)</span>
<span style="color: #000000;">k</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">length</span><span style="color: #0000FF;">(</span><span style="color: #000000;">idents</span><span style="color: #0000FF;">)</span>
<span style="color: #000000;">ididx</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">append</span><span style="color: #0000FF;">(</span><span style="color: #000000;">ididx</span><span style="color: #0000FF;">,</span><span style="color: #000000;">0</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">return</span> <span style="color: #000000;">k</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">function</span>
<span style="color: #008080;">forward</span> <span style="color: #008080;">function</span> <span style="color: #000000;">expression</span><span style="color: #0000FF;">()</span>
<span style="color: #008080;">function</span> <span style="color: #000000;">factor</span><span style="color: #0000FF;">()</span>
<span style="color: #004080;">object</span> <span style="color: #000000;">res</span>
<span style="color: #008080;">if</span> <span style="color: #004080;">sequence</span><span style="color: #0000FF;">(</span><span style="color: #000000;">token</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">then</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">token</span><span style="color: #0000FF;">[</span><span style="color: #000000;">1</span><span style="color: #0000FF;">]=</span><span style="color: #008000;">"ident"</span> <span style="color: #008080;">then</span>
<span style="color: #000000;">token</span> <span style="color: #0000FF;">&=</span> <span style="color: #000000;">add_ident</span><span style="color: #0000FF;">(</span><span style="color: #000000;">token</span><span style="color: #0000FF;">[</span><span style="color: #000000;">2</span><span style="color: #0000FF;">])</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #000000;">res</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">token</span>
<span style="color: #000000;">get_token</span><span style="color: #0000FF;">()</span>
<span style="color: #008080;">elsif</span> <span style="color: #000000;">token</span><span style="color: #0000FF;">=</span><span style="color: #008000;">'['</span> <span style="color: #008080;">then</span>
<span style="color: #000000;">get_token</span><span style="color: #0000FF;">()</span>
<span style="color: #000000;">res</span> <span style="color: #0000FF;">=</span> <span style="color: #0000FF;">{</span><span style="color: #008000;">"optional"</span><span style="color: #0000FF;">,</span><span style="color: #000000;">expression</span><span style="color: #0000FF;">()}</span>
<span style="color: #000000;">match_token</span><span style="color: #0000FF;">(</span><span style="color: #008000;">']'</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">elsif</span> <span style="color: #000000;">token</span><span style="color: #0000FF;">=</span><span style="color: #008000;">'('</span> <span style="color: #008080;">then</span>
<span style="color: #000000;">get_token</span><span style="color: #0000FF;">()</span>
<span style="color: #000000;">res</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">expression</span><span style="color: #0000FF;">()</span>
<span style="color: #000000;">match_token</span><span style="color: #0000FF;">(</span><span style="color: #008000;">')'</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">elsif</span> <span style="color: #000000;">token</span><span style="color: #0000FF;">=</span><span style="color: #008000;">'{'</span> <span style="color: #008080;">then</span>
<span style="color: #000000;">get_token</span><span style="color: #0000FF;">()</span>
<span style="color: #000000;">res</span> <span style="color: #0000FF;">=</span> <span style="color: #0000FF;">{</span><span style="color: #008000;">"repeat"</span><span style="color: #0000FF;">,</span><span style="color: #000000;">expression</span><span style="color: #0000FF;">()}</span>
<span style="color: #000000;">match_token</span><span style="color: #0000FF;">(</span><span style="color: #008000;">'}'</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">else</span>
<span style="color: #0000FF;">?</span><span style="color: #000000;">9</span><span style="color: #0000FF;">/</span><span style="color: #000000;">0</span> <span style="color: #000080;font-style:italic;">-- erm??
-- res = -1 -- ""</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">return</span> <span style="color: #000000;">res</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">function</span>
<span style="color: #008080;">function</span> <span style="color: #000000;">term</span><span style="color: #0000FF;">()</span>
<span style="color: #000080;font-style:italic;">-- sequence res = {"factors",factor()} -- (opted against this)</span>
<span style="color: #004080;">sequence</span> <span style="color: #000000;">res</span> <span style="color: #0000FF;">=</span> <span style="color: #0000FF;">{</span><span style="color: #000000;">factor</span><span style="color: #0000FF;">()}</span>
<span style="color: #008080;">while</span> <span style="color: #008080;">not</span> <span style="color: #7060A8;">find</span><span style="color: #0000FF;">(</span><span style="color: #000000;">token</span><span style="color: #0000FF;">,{-</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #008000;">'|'</span><span style="color: #0000FF;">,</span><span style="color: #008000;">'.'</span><span style="color: #0000FF;">,</span><span style="color: #008000;">';'</span><span style="color: #0000FF;">,</span><span style="color: #008000;">')'</span><span style="color: #0000FF;">,</span><span style="color: #008000;">']'</span><span style="color: #0000FF;">,</span><span style="color: #008000;">'}'</span><span style="color: #0000FF;">})</span> <span style="color: #008080;">do</span>
<span style="color: #000000;">res</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">append</span><span style="color: #0000FF;">(</span><span style="color: #000000;">res</span><span style="color: #0000FF;">,</span><span style="color: #000000;">factor</span><span style="color: #0000FF;">())</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">while</span>
<span style="color: #008080;">if</span> <span style="color: #7060A8;">length</span><span style="color: #0000FF;">(</span><span style="color: #000000;">res</span><span style="color: #0000FF;">)=</span><span style="color: #000000;">1</span> <span style="color: #008080;">then</span> <span style="color: #000000;">res</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">res</span><span style="color: #0000FF;">[</span><span style="color: #000000;">1</span><span style="color: #0000FF;">]</span> <span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">return</span> <span style="color: #000000;">res</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">function</span>
<span style="color: #008080;">function</span> <span style="color: #000000;">expression</span><span style="color: #0000FF;">()</span>
<span style="color: #004080;">object</span> <span style="color: #000000;">res</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">term</span><span style="color: #0000FF;">()</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">token</span><span style="color: #0000FF;">=</span><span style="color: #008000;">'|'</span> <span style="color: #008080;">then</span>
<span style="color: #000000;">res</span> <span style="color: #0000FF;">=</span> <span style="color: #0000FF;">{</span><span style="color: #008000;">"or"</span><span style="color: #0000FF;">,</span><span style="color: #000000;">res</span><span style="color: #0000FF;">}</span>
<span style="color: #008080;">while</span> <span style="color: #000000;">token</span><span style="color: #0000FF;">=</span><span style="color: #008000;">'|'</span> <span style="color: #008080;">do</span>
<span style="color: #000000;">get_token</span><span style="color: #0000FF;">()</span>
<span style="color: #000000;">res</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">append</span><span style="color: #0000FF;">(</span><span style="color: #000000;">res</span><span style="color: #0000FF;">,</span><span style="color: #000000;">term</span><span style="color: #0000FF;">())</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">while</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">return</span> <span style="color: #000000;">res</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">function</span>
<span style="color: #004080;">sequence</span> <span style="color: #000000;">productions</span> <span style="color: #0000FF;">=</span> <span style="color: #0000FF;">{}</span>
<span style="color: #008080;">function</span> <span style="color: #000000;">production</span><span style="color: #0000FF;">()</span>
<span style="color: #000080;font-style:italic;">-- returns a token or -1; the real result is left in productions[] etc.</span>
<span style="color: #000000;">get_token</span><span style="color: #0000FF;">()</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">token</span><span style="color: #0000FF;">!=</span><span style="color: #008000;">'}'</span> <span style="color: #008080;">then</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">token</span><span style="color: #0000FF;">=-</span><span style="color: #000000;">1</span> <span style="color: #008080;">then</span>
<span style="color: #008080;">return</span> <span style="color: #000000;">invalid</span><span style="color: #0000FF;">(</span><span style="color: #008000;">"invalid ebnf (missing closing })"</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">if</span> <span style="color: #008080;">not</span> <span style="color: #004080;">sequence</span><span style="color: #0000FF;">(</span><span style="color: #000000;">token</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">or</span> <span style="color: #000000;">token</span><span style="color: #0000FF;">[</span><span style="color: #000000;">1</span><span style="color: #0000FF;">]!=</span><span style="color: #008000;">"ident"</span> <span style="color: #008080;">then</span>
<span style="color: #008080;">return</span> <span style="color: #0000FF;">-</span><span style="color: #000000;">1</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #004080;">string</span> <span style="color: #000000;">ident</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">token</span><span style="color: #0000FF;">[</span><span style="color: #000000;">2</span><span style="color: #0000FF;">]</span>
<span style="color: #004080;">integer</span> <span style="color: #000000;">idx</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">add_ident</span><span style="color: #0000FF;">(</span><span style="color: #000000;">ident</span><span style="color: #0000FF;">)</span>
<span style="color: #000000;">get_token</span><span style="color: #0000FF;">()</span>
<span style="color: #000000;">match_token</span><span style="color: #0000FF;">(</span><span style="color: #008000;">'='</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">token</span><span style="color: #0000FF;">=-</span><span style="color: #000000;">1</span> <span style="color: #008080;">then</span>
<span style="color: #008080;">return</span> <span style="color: #0000FF;">-</span><span style="color: #000000;">1</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #004080;">sequence</span> <span style="color: #000000;">res</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">expression</span><span style="color: #0000FF;">()</span>
<span style="color: #000000;">productions</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">append</span><span style="color: #0000FF;">(</span><span style="color: #000000;">productions</span><span style="color: #0000FF;">,{</span><span style="color: #000000;">ident</span><span style="color: #0000FF;">,</span><span style="color: #000000;">idx</span><span style="color: #0000FF;">,</span><span style="color: #000000;">res</span><span style="color: #0000FF;">})</span>
<span style="color: #000000;">ididx</span><span style="color: #0000FF;">[</span><span style="color: #000000;">idx</span><span style="color: #0000FF;">]</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">length</span><span style="color: #0000FF;">(</span><span style="color: #000000;">productions</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">return</span> <span style="color: #000000;">token</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">function</span>
<span style="color: #004080;">sequence</span> <span style="color: #000000;">extras</span> <span style="color: #0000FF;">=</span> <span style="color: #0000FF;">{}</span>
<span style="color: #008080;">function</span> <span style="color: #000000;">parse</span><span style="color: #0000FF;">(</span><span style="color: #004080;">string</span> <span style="color: #000000;">ebnf</span><span style="color: #0000FF;">)</span>
<span style="color: #000080;font-style:italic;">-- returns: +1 if ok, -1 if bad</span>
<span style="color: #7060A8;">puts</span><span style="color: #0000FF;">(</span><span style="color: #000000;">1</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"parse: "</span><span style="color: #0000FF;">&</span><span style="color: #000000;">ebnf</span><span style="color: #0000FF;">&</span><span style="color: #008000;">" ===>\n"</span><span style="color: #0000FF;">)</span>
<span style="color: #000000;">error</span> <span style="color: #0000FF;">=</span> <span style="color: #004600;">false</span>
<span style="color: #000000;">src</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">ebnf</span>
<span style="color: #000000;">sdx</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">1</span>
<span style="color: #000000;">idents</span> <span style="color: #0000FF;">=</span> <span style="color: #0000FF;">{}</span>
<span style="color: #000000;">ididx</span> <span style="color: #0000FF;">=</span> <span style="color: #0000FF;">{}</span>
<span style="color: #000000;">productions</span> <span style="color: #0000FF;">=</span> <span style="color: #0000FF;">{}</span>
<span style="color: #000000;">extras</span> <span style="color: #0000FF;">=</span> <span style="color: #0000FF;">{}</span>
<span style="color: #000000;">get_token</span><span style="color: #0000FF;">()</span>
<span style="color: #008080;">if</span> <span style="color: #004080;">sequence</span><span style="color: #0000FF;">(</span><span style="color: #000000;">token</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">then</span>
<span style="color: #000000;">token</span><span style="color: #0000FF;">[</span><span style="color: #000000;">1</span><span style="color: #0000FF;">]</span> <span style="color: #0000FF;">=</span> <span style="color: #008000;">"title"</span>
<span style="color: #000000;">extras</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">append</span><span style="color: #0000FF;">(</span><span style="color: #000000;">extras</span><span style="color: #0000FF;">,</span><span style="color: #000000;">token</span><span style="color: #0000FF;">)</span>
<span style="color: #000000;">get_token</span><span style="color: #0000FF;">()</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">token</span><span style="color: #0000FF;">!=</span><span style="color: #008000;">'{'</span> <span style="color: #008080;">then</span>
<span style="color: #008080;">return</span> <span style="color: #000000;">invalid</span><span style="color: #0000FF;">(</span><span style="color: #008000;">"invalid ebnf (missing opening {)"</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">while</span> <span style="color: #000000;">1</span> <span style="color: #008080;">do</span>
<span style="color: #000000;">token</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">production</span><span style="color: #0000FF;">()</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">token</span><span style="color: #0000FF;">=</span><span style="color: #008000;">'}'</span> <span style="color: #008080;">or</span> <span style="color: #000000;">token</span><span style="color: #0000FF;">=-</span><span style="color: #000000;">1</span> <span style="color: #008080;">then</span> <span style="color: #008080;">exit</span> <span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">while</span>
<span style="color: #000000;">get_token</span><span style="color: #0000FF;">()</span>
<span style="color: #008080;">if</span> <span style="color: #004080;">sequence</span><span style="color: #0000FF;">(</span><span style="color: #000000;">token</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">then</span>
<span style="color: #000000;">token</span><span style="color: #0000FF;">[</span><span style="color: #000000;">1</span><span style="color: #0000FF;">]</span> <span style="color: #0000FF;">=</span> <span style="color: #008000;">"comment"</span>
<span style="color: #000000;">extras</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">append</span><span style="color: #0000FF;">(</span><span style="color: #000000;">extras</span><span style="color: #0000FF;">,</span><span style="color: #000000;">token</span><span style="color: #0000FF;">)</span>
<span style="color: #000000;">get_token</span><span style="color: #0000FF;">()</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">token</span><span style="color: #0000FF;">!=-</span><span style="color: #000000;">1</span> <span style="color: #008080;">then</span>
<span style="color: #008080;">return</span> <span style="color: #000000;">invalid</span><span style="color: #0000FF;">(</span><span style="color: #008000;">"invalid ebnf (missing eof?)"</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">error</span> <span style="color: #008080;">then</span> <span style="color: #008080;">return</span> <span style="color: #0000FF;">-</span><span style="color: #000000;">1</span> <span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #004080;">integer</span> <span style="color: #000000;">k</span> <span style="color: #0000FF;">=</span> <span style="color: #7060A8;">find</span><span style="color: #0000FF;">(</span><span style="color: #000000;">0</span><span style="color: #0000FF;">,</span><span style="color: #000000;">ididx</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">k</span><span style="color: #0000FF;">!=</span><span style="color: #000000;">0</span> <span style="color: #008080;">then</span>
<span style="color: #008080;">return</span> <span style="color: #000000;">invalid</span><span style="color: #0000FF;">(</span><span style="color: #008000;">"invalid ebnf (undefined:"</span><span style="color: #0000FF;">&</span><span style="color: #000000;">idents</span><span style="color: #0000FF;">[</span><span style="color: #000000;">k</span><span style="color: #0000FF;">]&</span><span style="color: #008000;">")"</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #7060A8;">ppOpt</span><span style="color: #0000FF;">({</span><span style="color: #004600;">pp_Pause</span><span style="color: #0000FF;">,</span><span style="color: #000000;">0</span><span style="color: #0000FF;">})</span>
<span style="color: #7060A8;">pp</span><span style="color: #0000FF;">(</span><span style="color: #000000;">productions</span><span style="color: #0000FF;">)</span>
<span style="color: #000080;font-style:italic;">-- pp(idents)
-- pp(ididx)
-- pp(extras)</span>
<span style="color: #008080;">return</span> <span style="color: #000000;">1</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">function</span>
<span style="color: #000080;font-style:italic;">-- The rules that applies() has to deal with are:
-- {factors} - if rule[1] is not string, just apply one after the other,
-- recursively. As per term() above, originally had "factors",
-- but getting rid of it made the syntax tree much clearer)
-- {"terminal", "a1"} -- literal constants
-- {"or", <e1>, <e2>, ...} -- (any) one of n
-- {"repeat", <e1>} -- as per "{}" in ebnf
-- {"optional", <e1>} -- as per "[]" in ebnf
-- {"ident", <name>, idx} -- apply the sub-rule</span>
<span style="color: #008080;">function</span> <span style="color: #000000;">applies</span><span style="color: #0000FF;">(</span><span style="color: #004080;">sequence</span> <span style="color: #000000;">rule</span><span style="color: #0000FF;">)</span>
<span style="color: #004080;">integer</span> <span style="color: #000000;">was_sdx</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">sdx</span> <span style="color: #000080;font-style:italic;">-- in case of failure</span>
<span style="color: #004080;">object</span> <span style="color: #000000;">r1</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">rule</span><span style="color: #0000FF;">[</span><span style="color: #000000;">1</span><span style="color: #0000FF;">]</span>
<span style="color: #008080;">if</span> <span style="color: #008080;">not</span> <span style="color: #004080;">string</span><span style="color: #0000FF;">(</span><span style="color: #000000;">r1</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">then</span>
<span style="color: #008080;">for</span> <span style="color: #000000;">i</span><span style="color: #0000FF;">=</span><span style="color: #000000;">1</span> <span style="color: #008080;">to</span> <span style="color: #7060A8;">length</span><span style="color: #0000FF;">(</span><span style="color: #000000;">rule</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">do</span>
<span style="color: #008080;">if</span> <span style="color: #008080;">not</span> <span style="color: #000000;">applies</span><span style="color: #0000FF;">(</span><span style="color: #000000;">rule</span><span style="color: #0000FF;">[</span><span style="color: #000000;">i</span><span style="color: #0000FF;">])</span> <span style="color: #008080;">then</span>
<span style="color: #000000;">sdx</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">was_sdx</span>
<span style="color: #008080;">return</span> <span style="color: #004600;">false</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">for</span>
<span style="color: #008080;">elsif</span> <span style="color: #000000;">r1</span><span style="color: #0000FF;">=</span><span style="color: #008000;">"terminal"</span> <span style="color: #008080;">then</span>
<span style="color: #000000;">skip_spaces</span><span style="color: #0000FF;">()</span>
<span style="color: #008080;">for</span> <span style="color: #000000;">i</span><span style="color: #0000FF;">=</span><span style="color: #000000;">1</span> <span style="color: #008080;">to</span> <span style="color: #7060A8;">length</span><span style="color: #0000FF;">(</span><span style="color: #000000;">rule</span><span style="color: #0000FF;">[</span><span style="color: #000000;">2</span><span style="color: #0000FF;">])</span> <span style="color: #008080;">do</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">sdx</span><span style="color: #0000FF;">></span><span style="color: #7060A8;">length</span><span style="color: #0000FF;">(</span><span style="color: #000000;">src</span><span style="color: #0000FF;">)</span>
<span style="color: #008080;">or</span> <span style="color: #000000;">src</span><span style="color: #0000FF;">[</span><span style="color: #000000;">sdx</span><span style="color: #0000FF;">]!=</span><span style="color: #000000;">rule</span><span style="color: #0000FF;">[</span><span style="color: #000000;">2</span><span style="color: #0000FF;">][</span><span style="color: #000000;">i</span><span style="color: #0000FF;">]</span> <span style="color: #008080;">then</span>
<span style="color: #000000;">sdx</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">was_sdx</span>
<span style="color: #008080;">return</span> <span style="color: #004600;">false</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #000000;">sdx</span> <span style="color: #0000FF;">+=</span> <span style="color: #000000;">1</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">for</span>
<span style="color: #008080;">elsif</span> <span style="color: #000000;">r1</span><span style="color: #0000FF;">=</span><span style="color: #008000;">"or"</span> <span style="color: #008080;">then</span>
<span style="color: #008080;">for</span> <span style="color: #000000;">i</span><span style="color: #0000FF;">=</span><span style="color: #000000;">2</span> <span style="color: #008080;">to</span> <span style="color: #7060A8;">length</span><span style="color: #0000FF;">(</span><span style="color: #000000;">rule</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">do</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">applies</span><span style="color: #0000FF;">(</span><span style="color: #000000;">rule</span><span style="color: #0000FF;">[</span><span style="color: #000000;">i</span><span style="color: #0000FF;">])</span> <span style="color: #008080;">then</span>
<span style="color: #008080;">return</span> <span style="color: #004600;">true</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">for</span>
<span style="color: #000000;">sdx</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">was_sdx</span>
<span style="color: #008080;">return</span> <span style="color: #004600;">false</span>
<span style="color: #008080;">elsif</span> <span style="color: #000000;">r1</span><span style="color: #0000FF;">=</span><span style="color: #008000;">"repeat"</span> <span style="color: #008080;">then</span>
<span style="color: #008080;">while</span> <span style="color: #000000;">applies</span><span style="color: #0000FF;">(</span><span style="color: #000000;">rule</span><span style="color: #0000FF;">[</span><span style="color: #000000;">2</span><span style="color: #0000FF;">])</span> <span style="color: #008080;">do</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">while</span>
<span style="color: #008080;">elsif</span> <span style="color: #000000;">r1</span><span style="color: #0000FF;">=</span><span style="color: #008000;">"optional"</span> <span style="color: #008080;">then</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">applies</span><span style="color: #0000FF;">(</span><span style="color: #000000;">rule</span><span style="color: #0000FF;">[</span><span style="color: #000000;">2</span><span style="color: #0000FF;">])</span> <span style="color: #008080;">then</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">elsif</span> <span style="color: #000000;">r1</span><span style="color: #0000FF;">=</span><span style="color: #008000;">"ident"</span> <span style="color: #008080;">then</span>
<span style="color: #004080;">integer</span> <span style="color: #000000;">i</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">rule</span><span style="color: #0000FF;">[</span><span style="color: #000000;">3</span><span style="color: #0000FF;">],</span>
<span style="color: #000000;">ii</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">ididx</span><span style="color: #0000FF;">[</span><span style="color: #000000;">i</span><span style="color: #0000FF;">]</span>
<span style="color: #008080;">if</span> <span style="color: #008080;">not</span> <span style="color: #000000;">applies</span><span style="color: #0000FF;">(</span><span style="color: #000000;">productions</span><span style="color: #0000FF;">[</span><span style="color: #000000;">ii</span><span style="color: #0000FF;">][</span><span style="color: #000000;">3</span><span style="color: #0000FF;">])</span> <span style="color: #008080;">then</span>
<span style="color: #000000;">sdx</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">was_sdx</span>
<span style="color: #008080;">return</span> <span style="color: #004600;">false</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">else</span>
<span style="color: #0000FF;">?</span><span style="color: #000000;">9</span><span style="color: #0000FF;">/</span><span style="color: #000000;">0</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">return</span> <span style="color: #004600;">true</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">function</span>
<span style="color: #008080;">procedure</span> <span style="color: #000000;">check_valid</span><span style="color: #0000FF;">(</span><span style="color: #004080;">string</span> <span style="color: #000000;">test</span><span style="color: #0000FF;">)</span>
<span style="color: #000000;">src</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">test</span>
<span style="color: #000000;">sdx</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">1</span>
<span style="color: #004080;">bool</span> <span style="color: #000000;">res</span> <span style="color: #0000FF;">=</span> <span style="color: #000000;">applies</span><span style="color: #0000FF;">(</span><span style="color: #000000;">productions</span><span style="color: #0000FF;">[</span><span style="color: #000000;">1</span><span style="color: #0000FF;">][</span><span style="color: #000000;">3</span><span style="color: #0000FF;">])</span>
<span style="color: #000000;">skip_spaces</span><span style="color: #0000FF;">()</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">sdx</span><span style="color: #0000FF;"><=</span><span style="color: #7060A8;">length</span><span style="color: #0000FF;">(</span><span style="color: #000000;">src</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">then</span> <span style="color: #000000;">res</span> <span style="color: #0000FF;">=</span> <span style="color: #004600;">false</span> <span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #0000FF;">?{</span><span style="color: #000000;">test</span><span style="color: #0000FF;">,{</span><span style="color: #008000;">"pass"</span><span style="color: #0000FF;">,</span><span style="color: #008000;">"fail"</span><span style="color: #0000FF;">}[</span><span style="color: #000000;">2</span><span style="color: #0000FF;">-</span><span style="color: #000000;">res</span><span style="color: #0000FF;">]}</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">procedure</span>
<span style="color: #008080;">constant</span> <span style="color: #000000;">ebnf</span> <span style="color: #0000FF;">=</span> <span style="color: #0000FF;">{</span><span style="color: #008000;">"""
"a" {
a = "a1" ( "a2" | "a3" ) { "a4" } [ "a5" ] "a6" ;
} "z" """</span><span style="color: #0000FF;">,</span>
<span style="color: #008000;">"""
{
expr = term { plus term } .
term = factor { times factor } .
factor = number | '(' expr ')' .
plus = "+" | "-" .
times = "*" | "/" .
number = digit { digit } .
digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" .
}"""</span><span style="color: #0000FF;">,</span>
<span style="color: #008000;">`a = "1"`</span><span style="color: #0000FF;">,</span>
<span style="color: #008000;">`{ a = "1" ;`</span><span style="color: #0000FF;">,</span>
<span style="color: #008000;">`{ hello world = "1"; }`</span><span style="color: #0000FF;">,</span>
<span style="color: #008000;">`{ foo = bar . }`</span>
<span style="color: #0000FF;">}</span>
<span style="color: #008080;">constant</span> <span style="color: #000000;">tests</span> <span style="color: #0000FF;">=</span> <span style="color: #0000FF;">{</span> <span style="color: #0000FF;">{</span><span style="color: #008000;">"a1a3a4a4a5a6"</span><span style="color: #0000FF;">,</span>
<span style="color: #008000;">"a1 a2a6"</span><span style="color: #0000FF;">,</span>
<span style="color: #008000;">"a1 a3 a4 a6"</span><span style="color: #0000FF;">,</span>
<span style="color: #008000;">"a1 a4 a5 a6"</span><span style="color: #0000FF;">,</span>
<span style="color: #008000;">"a1 a2 a4 a5 a5 a6"</span><span style="color: #0000FF;">,</span>
<span style="color: #008000;">"a1 a2 a4 a5 a6 a7"</span><span style="color: #0000FF;">,</span>
<span style="color: #008000;">"your ad here"</span><span style="color: #0000FF;">},</span>
<span style="color: #0000FF;">{</span><span style="color: #008000;">"2"</span><span style="color: #0000FF;">,</span>
<span style="color: #008000;">"2*3 + 4/23 - 7"</span><span style="color: #0000FF;">,</span>
<span style="color: #008000;">"(3 + 4) * 6-2+(4*(4))"</span><span style="color: #0000FF;">,</span>
<span style="color: #008000;">"-2"</span><span style="color: #0000FF;">,</span>
<span style="color: #008000;">"3 +"</span><span style="color: #0000FF;">,</span>
<span style="color: #008000;">"(4 + 3"</span><span style="color: #0000FF;">}}</span>
<span style="color: #008080;">for</span> <span style="color: #000000;">i</span><span style="color: #0000FF;">=</span><span style="color: #000000;">1</span> <span style="color: #008080;">to</span> <span style="color: #7060A8;">length</span><span style="color: #0000FF;">(</span><span style="color: #000000;">ebnf</span><span style="color: #0000FF;">)</span> <span style="color: #008080;">do</span>
<span style="color: #008080;">if</span> <span style="color: #000000;">parse</span><span style="color: #0000FF;">(</span><span style="color: #000000;">ebnf</span><span style="color: #0000FF;">[</span><span style="color: #000000;">i</span><span style="color: #0000FF;">])=+</span><span style="color: #000000;">1</span> <span style="color: #008080;">then</span>
<span style="color: #0000FF;">?</span><span style="color: #008000;">"tests:"</span>
<span style="color: #008080;">for</span> <span style="color: #000000;">j</span><span style="color: #0000FF;">=</span><span style="color: #000000;">1</span> <span style="color: #008080;">to</span> <span style="color: #7060A8;">length</span><span style="color: #0000FF;">(</span><span style="color: #000000;">tests</span><span style="color: #0000FF;">[</span><span style="color: #000000;">i</span><span style="color: #0000FF;">])</span> <span style="color: #008080;">do</span>
<span style="color: #000000;">check_valid</span><span style="color: #0000FF;">(</span><span style="color: #000000;">tests</span><span style="color: #0000FF;">[</span><span style="color: #000000;">i</span><span style="color: #0000FF;">][</span><span style="color: #000000;">j</span><span style="color: #0000FF;">])</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">for</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">if</span>
<span style="color: #008080;">end</span> <span style="color: #008080;">for</span>
<!--</syntaxhighlight>-->
In real use, I would be tempted to use numeric literals rather than string tags in such structures, but the latter certainly make things ten times easier to debug, plus I got an instantly legible syntax tree dump (the bit just after "===>" below) practically for free.
{{out}}
<pre>
parse:
"a" {
a = "a1" ( "a2" | "a3" ) { "a4" } [ "a5" ] "a6" ;
} "z" ===>
{{"a", 1,
{{"terminal", "a1"}, {"or", {"terminal", "a2"}, {"terminal", "a3"}},
{"repeat", {"terminal", "a4"}}, {"optional", {"terminal", "a5"}},
{"terminal", "a6"}}}}
"tests:"
{"a1a3a4a4a5a6","pass"}
{"a1 a2a6","pass"}
{"a1 a3 a4 a6","pass"}
{"a1 a4 a5 a6","fail"}
{"a1 a2 a4 a5 a5 a6","fail"}
{"a1 a2 a4 a5 a6 a7","fail"}
{"your ad here","fail"}
parse:
{
expr = term { plus term } .
term = factor { times factor } .
factor = number | '(' expr ')' .
plus = "+" | "-" .
times = "*" | "/" .
number = digit { digit } .
digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" .
} ===>
{{"expr", 1,
{{"ident", "term", 2},
{"repeat", {{"ident", "plus", 3}, {"ident", "term", 2}}}}},
{"term", 2,
{{"ident", "factor", 4},
{"repeat", {{"ident", "times", 5}, {"ident", "factor", 4}}}}},
{"factor", 4,
{"or", {"ident", "number", 6},
{{"terminal", "("}, {"ident", "expr", 1}, {"terminal", ")"}}}},
{"plus", 3, {"or", {"terminal", "+"}, {"terminal", "-"}}},
{"times", 5, {"or", {"terminal", "*"}, {"terminal", "/"}}},
{"number", 6, {{"ident", "digit", 7}, {"repeat", {"ident", "digit", 7}}}},
{"digit", 7,
{"or", {"terminal", "0"}, {"terminal", "1"}, {"terminal", "2"},
{"terminal", "3"}, {"terminal", "4"}, {"terminal", "5"},
{"terminal", "6"}, {"terminal", "7"}, {"terminal", "8"},
{"terminal", "9"}}}}
"tests:"
{"2","pass"}
{"2*3 + 4/23 - 7","pass"}
{"(3 + 4) * 6-2+(4*(4))","pass"}
{"-2","fail"}
{"3 +","fail"}
{"(4 + 3","fail"}
parse: a = "1" ===>
"invalid ebnf (missing opening {)"
parse: { a = "1" ; ===>
"invalid ebnf (missing closing })"
parse: { hello world = "1"; } ===>
"invalid ebnf (= expected)"
parse: { foo = bar . } ===>
"invalid ebnf (undefined:bar)"
</pre>
=={{header|PicoLisp}}==
<syntaxhighlight lang="picolisp">(de EBNF
"expr : term ( ( PLUS | MINUS ) term )* ;"
"term : factor ( ( MULT | DIV ) factor )* ;"
"factor : NUMBER ;" )
(for E EBNF
(use (@S @E)
(unless (and (match '(@S : @E ;) (str E)) (not (cdr @S)))
(quit "Invalid EBNF" E) )
(put (car @S) 'ebnf @E) ) )</syntaxhighlight>
<syntaxhighlight lang="picolisp">(de matchEbnf (Pat)
(cond
((asoq Pat '((PLUS . +) (MINUS . -) (MULT . *) (DIV . /)))
(let Op (cdr @)
(when (= Op (car *Lst))
(pop '*Lst)
Op ) ) )
((== 'NUMBER Pat)
(cond
((num? (car *Lst))
(pop '*Lst)
@ )
((and (= "-" (car *Lst)) (num? (cadr *Lst)))
(setq *Lst (cddr *Lst))
(- @) ) ) )
((get Pat 'ebnf) (parseLst @))
((atom Pat))
(T
(loop
(T (matchEbnf (pop 'Pat)) @)
(NIL Pat)
(NIL (== '| (pop 'Pat)))
(NIL Pat) ) ) ) )
(de parseLst (Pat)
(let (P (pop 'Pat) X (matchEbnf P))
(loop
(NIL Pat)
(if (n== '* (cadr Pat))
(if (matchEbnf (pop 'Pat))
(setq X (list @ X))
(throw) )
(loop
(NIL *Lst)
(NIL (matchEbnf (car Pat)))
(setq X (list @ X (or (matchEbnf P) (throw)))) )
(setq Pat (cddr Pat)) ) )
X ) )
(de parseEbnf (Str)
(let *Lst (str Str "")
(catch NIL
(parseLst (get 'expr 'ebnf)) ) ) )</syntaxhighlight>
Output:
<pre>: (parseEbnf "1 + 2 * -3 / 7 - 3 * 4")
-> (- (+ 1 (/ (* 2 -3) 7)) (* 3 4))</pre>
=={{header|Raku}}==
(formerly Perl 6)
{{works with|Rakudo|2019.03.1}}
This parses the EBNF rule set using a Raku grammar, then if it parses as valid EBNF, constructs a grammar and parses the test strings with that. EBNF rule sets that are naively syntactically correct but missing rules will parse as valid but will give a runtime failure warning about missing methods.
It is implemented and exercised using the flavor of EBNF and test cases specified on the [[Parse EBNF/Tests|test page]].
<syntaxhighlight lang="raku" line># A Raku grammar to parse EBNF
grammar EBNF {
rule TOP { ^ <title>? '{' [ <production> ]+ '}' <comment>? $ }
rule production { <name> '=' <expression> <[.;]> }
rule expression { <term> +% "|" }
rule term { <factor>+ }
rule factor { <group> | <repeat> | <optional> | <identifier> | <literal> }
rule group { '(' <expression> ')' }
rule repeat { '{' <expression> '}' }
rule optional { '[' <expression> ']' }
token identifier { <-[\|\(\)\{\}\[\]\.\;\"\'\s]>+ } #"
token literal { ["'" <-[']>+ "'" | '"' <-["]>+ '"'] } #"
token title { <literal> }
token comment { <literal> }
token name { <identifier> <?before \h* '='> }
}
class EBNF::Actions {
method TOP($/) {
say "Syntax Tree:\n", $/; # Dump the syntax tree to STDOUT
make 'grammar ' ~
($<title> ?? $<title>.subst(/\W/, '', :g) !! 'unnamed') ~
" \{\n rule TOP \{^[<" ~ $/<production>[0]<name> ~
">]+\$\}\n " ~ $<production>>>.ast ~ "\}"
}
method production($/) {
make 'token ' ~ $<name> ~ ' {' ~
$<expression>.ast ~ "}\n"
}
method expression($/) { make join '|', $<term>>>.ast }
method term($/) { make join '\h*', $<factor>>>.ast }
method factor($/) {
make $<literal> ?? $<literal> !!
$<group> ?? '[' ~ $<group>.ast ~ ']' !!
$<repeat> ?? '[' ~ $<repeat>.ast ~ '\\s*]*' !!
$<optional> ?? '[' ~ $<optional>.ast ~ ']?' !!
'<' ~ $<identifier> ~ '>'
}
method repeat($/) { make $<expression>.ast }
method optional($/) { make $<expression>.ast }
method group($/) { make $<expression>.ast }
}
# An array of test cases
my @tests = (
{
ebnf =>
q<"a" {
a = "a1" ( "a2" | "a3" ) { "a4" } [ "a5" ] "a6" ;
} "z">
,
teststrings => [
'a1a3a4a4a5a6',
'a1 a2a6',
'a1 a3 a4 a6',
'a1 a4 a5 a6',
'a1 a2 a4 a4 a5 a6',
'a1 a2 a4 a5 a5 a6',
'a1 a2 a4 a5 a6 a7',
'your ad here'
]
},
{
ebnf =>
q<{
expr = term { plus term } .
term = factor { times factor } .
factor = number | '(' expr ')' .
plus = "+" | "-" .
times = "*" | "/" .
number = digit { digit } .
digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" .
}>
,
teststrings => [
'2',
'2*3 + 4/23 - 7',
'(3 + 4) * 6-2+(4*(4))',
'-2',
'3 +',
'(4 + 3'
]
},
{
ebnf => q<a = "1";>,
teststrings => ['foobar']
},
{
ebnf => q<{ a = "1" ;>,
teststrings => ['foobar']
},
{
ebnf => q<{ hello world = "1"; }>,
teststrings => ['foobar']
},
{
ebnf => q<{ foo = bar . }>,
teststrings => ['foobar']
}
);
# Test the parser.
my $i = 1;
for @tests -> $test {
unless EBNF.parse($test<ebnf>) {
say "Parsing EBNF grammar:\n";
say "{$test<ebnf>.subst(/^^\h*/,'',:g)}\n";
say "Invalid syntax. Can not be parsed.\n";
say '*' x 79;
next;
}
my $p = EBNF.parse($test<ebnf>, :actions(EBNF::Actions));
my $grammar = $p.ast;
$grammar ~~ m/^'grammar '(\w+)/;
my $title = $0;
my $fn = 'EBNFtest'~$i++;
my $fh = open($fn, :w) orelse .die;
$fh.say( "\{\n", $grammar );
$fh.say( qq|say "Parsing EBNF grammar '$title':\\n";| );
$fh.say( qq|say q<{$test<ebnf>.subst(/^^\h*/,'',:g)}>;| );
$fh.say( q|say "\nValid syntax.\n\nTesting:\n";| );
$fh.say( q|CATCH { default { say " - $_" } };| );
my $len = max $test<teststrings>.flat>>.chars;
for $test<teststrings>.flat -> $s {
$fh.say( qq|printf "%{$len}s", '{$s}';| ~
qq|printf " - %s\\n", {$title}.parse('{$s}')| ~
qq| ?? 'valid.' !! 'NOT valid.';|
);
}
$fh.say( qq| "\\n"} |);
$fh.close;
say qqx/raku $fn/;
say '*' x 79, "\n";
unlink $fn;
}</syntaxhighlight>
Output:
<pre>
Syntax Tree:
｢"a" {
a = "a1" ( "a2" | "a3" ) { "a4" } [ "a5" ] "a6" ;
} "z"｣
title => ｢"a"｣
literal => ｢"a"｣
production => ｢a = "a1" ( "a2" | "a3" ) { "a4" } [ "a5" ] "a6" ;
｣
name => ｢a｣
identifier => ｢a｣
expression => ｢"a1" ( "a2" | "a3" ) { "a4" } [ "a5" ] "a6" ｣
term => ｢"a1" ( "a2" | "a3" ) { "a4" } [ "a5" ] "a6" ｣
factor => ｢"a1" ｣
literal => ｢"a1"｣
factor => ｢( "a2" | "a3" ) ｣
group => ｢( "a2" | "a3" ) ｣
expression => ｢"a2" | "a3" ｣
term => ｢"a2" ｣
factor => ｢"a2" ｣
literal => ｢"a2"｣
term => ｢ "a3" ｣
factor => ｢"a3" ｣
literal => ｢"a3"｣
factor => ｢{ "a4" } ｣
repeat => ｢{ "a4" } ｣
expression => ｢"a4" ｣
term => ｢"a4" ｣
factor => ｢"a4" ｣
literal => ｢"a4"｣
factor => ｢[ "a5" ] ｣
optional => ｢[ "a5" ] ｣
expression => ｢"a5" ｣
term => ｢"a5" ｣
factor => ｢"a5" ｣
literal => ｢"a5"｣
factor => ｢"a6" ｣
literal => ｢"a6"｣
comment => ｢"z"｣
literal => ｢"z"｣
Parsing EBNF grammar 'a':
"a" {
a = "a1" ( "a2" | "a3" ) { "a4" } [ "a5" ] "a6" ;
} "z"
Valid syntax.
Testing:
a1a3a4a4a5a6 - valid.
a1 a2a6 - valid.
a1 a3 a4 a6 - valid.
a1 a4 a5 a6 - NOT valid.
a1 a2 a4 a4 a5 a6 - valid.
a1 a2 a4 a5 a5 a6 - NOT valid.
a1 a2 a4 a5 a6 a7 - NOT valid.
your ad here - NOT valid.
*******************************************************************************
Syntax Tree:
｢{
expr = term { plus term } .
term = factor { times factor } .
factor = number | '(' expr ')' .
plus = "+" | "-" .
times = "*" | "/" .
number = digit { digit } .
digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" .
}｣
production => ｢expr = term { plus term } .
｣
name => ｢expr｣
identifier => ｢expr｣
expression => ｢term { plus term } ｣
term => ｢term { plus term } ｣
factor => ｢term ｣
identifier => ｢term｣
factor => ｢{ plus term } ｣
repeat => ｢{ plus term } ｣
expression => ｢plus term ｣
term => ｢plus term ｣
factor => ｢plus ｣
identifier => ｢plus｣
factor => ｢term ｣
identifier => ｢term｣
production => ｢term = factor { times factor } .
｣
name => ｢term｣
identifier => ｢term｣
expression => ｢factor { times factor } ｣
term => ｢factor { times factor } ｣
factor => ｢factor ｣
identifier => ｢factor｣
factor => ｢{ times factor } ｣
repeat => ｢{ times factor } ｣
expression => ｢times factor ｣
term => ｢times factor ｣
factor => ｢times ｣
identifier => ｢times｣
factor => ｢factor ｣
identifier => ｢factor｣
production => ｢factor = number | '(' expr ')' .
｣
name => ｢factor｣
identifier => ｢factor｣
expression => ｢number | '(' expr ')' ｣
term => ｢number ｣
factor => ｢number ｣
identifier => ｢number｣
term => ｢ '(' expr ')' ｣
factor => ｢'(' ｣
literal => ｢'('｣
factor => ｢expr ｣
identifier => ｢expr｣
factor => ｢')' ｣
literal => ｢')'｣
production => ｢plus = "+" | "-" .
｣
name => ｢plus｣
identifier => ｢plus｣
expression => ｢"+" | "-" ｣
term => ｢"+" ｣
factor => ｢"+" ｣
literal => ｢"+"｣
term => ｢ "-" ｣
factor => ｢"-" ｣
literal => ｢"-"｣
production => ｢times = "*" | "/" .
｣
name => ｢times｣
identifier => ｢times｣
expression => ｢"*" | "/" ｣
term => ｢"*" ｣
factor => ｢"*" ｣
literal => ｢"*"｣
term => ｢ "/" ｣
factor => ｢"/" ｣
literal => ｢"/"｣
production => ｢number = digit { digit } .
｣
name => ｢number｣
identifier => ｢number｣
expression => ｢digit { digit } ｣
term => ｢digit { digit } ｣
factor => ｢digit ｣
identifier => ｢digit｣
factor => ｢{ digit } ｣
repeat => ｢{ digit } ｣
expression => ｢digit ｣
term => ｢digit ｣
factor => ｢digit ｣
identifier => ｢digit｣
production => ｢digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" .
｣
name => ｢digit｣
identifier => ｢digit｣
expression => ｢"0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" ｣
term => ｢"0" ｣
factor => ｢"0" ｣
literal => ｢"0"｣
term => ｢ "1" ｣
factor => ｢"1" ｣
literal => ｢"1"｣
term => ｢ "2" ｣
factor => ｢"2" ｣
literal => ｢"2"｣
term => ｢ "3" ｣
factor => ｢"3" ｣
literal => ｢"3"｣
term => ｢ "4" ｣
factor => ｢"4" ｣
literal => ｢"4"｣
term => ｢ "5" ｣
factor => ｢"5" ｣
literal => ｢"5"｣
term => ｢ "6" ｣
factor => ｢"6" ｣
literal => ｢"6"｣
term => ｢ "7" ｣
factor => ｢"7" ｣
literal => ｢"7"｣
term => ｢ "8" ｣
factor => ｢"8" ｣
literal => ｢"8"｣
term => ｢ "9" ｣
factor => ｢"9" ｣
literal => ｢"9"｣
Parsing EBNF grammar 'unnamed':
{
expr = term { plus term } .
term = factor { times factor } .
factor = number | '(' expr ')' .
plus = "+" | "-" .
times = "*" | "/" .
number = digit { digit } .
digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" .
}
Valid syntax.
Testing:
2 - valid.
2*3 + 4/23 - 7 - valid.
(3 + 4) * 6-2+(4*(4)) - valid.
-2 - NOT valid.
3 + - NOT valid.
(4 + 3 - NOT valid.
*******************************************************************************
Parsing EBNF grammar:
a = "1";
Invalid syntax. Can not be parsed.
*******************************************************************************
Parsing EBNF grammar:
{ a = "1" ;
Invalid syntax. Can not be parsed.
*******************************************************************************
Parsing EBNF grammar:
{ hello world = "1"; }
Invalid syntax. Can not be parsed.
*******************************************************************************
Syntax Tree:
｢{ foo = bar . }｣
production => ｢foo = bar . ｣
name => ｢foo｣
identifier => ｢foo｣
expression => ｢bar ｣
term => ｢bar ｣
factor => ｢bar ｣
identifier => ｢bar｣
Parsing EBNF grammar 'unnamed':
{ foo = bar . }
Valid syntax.
Testing:
foobar - No such method 'bar' for invocant of type 'unnamed'
*******************************************************************************</pre>
=={{header|Ruby}}==
{{in progress|lang=Ruby|day=12|month=May|year=2011}}
{{incomplete|Ruby|The tokenizer is here, but the parser is very incomplete.}}
<syntaxhighlight lang="ruby">#--
# The tokenizer splits the input into Tokens like "identifier",
# ":", ")*" and so on. This design uses a StringScanner on each line of
# input, therefore a Token can never span more than one line.
#
# Each Token knows its original line and position, so an error message
# can locate a bad token.
#++
require 'strscan'
# A line of input.
# where:: A location like "file.txt:3"
# str:: String of this line
Line = Struct.new :where, :str
# A token.
# cat:: A category like :colon, :ident or so on
# str:: String of this token
# line:: Line containing this token
# pos:: Position of this token within this line
Token = Struct.new :cat, :str, :line, :pos
# Reads and returns the next Token. At end of file, returns nil.
#--
# Needs @filename and @in.
#++
def next_token
# Loop until we reach a Token.
loop do
# If at end of line, then get next line, or else declare end of
# file.
if @scanner.eos?
if s = @in.gets
# Each line needs a new Line object. Tokens can hold references
# to old Line objects.
@line = Line.new("#{@filename}:#{@in.lineno}", s)
@scanner.string = s
else
return nil # End of file
end
end
# Skip whitespace.
break unless @scanner.skip(/[[:space:]]+/)
end
# Read token by regular expression.
if s = @scanner.scan(/:/)
c = :colon
elsif s = @scanner.scan(/;/)
c = :semicolon
elsif s = @scanner.scan(/\(/)
c = :paren
elsif s = @scanner.scan(/\)\?/)
c = :option
elsif s = @scanner.scan(/\)\*/)
c = :repeat
elsif s = @scanner.scan(/\)/)
c = :group
elsif s = @scanner.scan(/\|/)
c = :bar
elsif s = @scanner.scan(/[[:alpha:]][[:alnum:]]*/)
c = :ident
elsif s = @scanner.scan(/'[^']*'|"[^"]*"/)
# Fix syntax highlighting for Rosetta Code. => '
c = :string
elsif s = @scanner.scan(/'[^']*|"[^"]*/)
c = :bad_string
elsif s = @scanner.scan(/.*/)
c = :unknown
end
Token.new(c, s, @line, (@scanner.pos - s.length))
end
# Prints a _message_ to standard error, along with location of _token_.
def error(token, message)
line = token.line
# We print a caret ^ pointing at the bad token. We make a very crude
# attempt to align the caret ^ in the correct column. If the input
# line has a non-[:print:] character, like a tab, then we print it as
# a space.
STDERR.puts <<EOF
#{line.where}: #{message}
#{line.str.gsub(/[^[:print:]]/, " ")}
#{" " * token.pos}^
EOF
end
#--
# The parser converts Tokens to a Grammar object. The parser also
# detects syntax errors.
#++
# A parsed EBNF grammar. It is an Array of Productions.
class Grammar < Array; end
# A production.
# ident:: The identifier
# alts:: An Array of Alternatives
Production = Struct.new :ident, :alts
# An array of Alternatives, as from "(a | b)".
class Group < Array; end
# An optional group, as from "(a | b)?".
class OptionalGroup < Group; end
# A repeated group, as from "(a | b)*".
class RepeatedGroup < Group; end
# An array of identifiers and string literals.
class Alternative < Array; end
#--
# Needs @filename and @in.
#++
def parse
# TODO: this only dumps the tokens.
while t = next_token
error(t, "#{t.cat}")
end
end
# Set @filename and @in. Parse input.
case ARGV.length
when 0 then @filename = "-"
when 1 then @filename = ARGV[0]
else fail "Too many arguments"
end
open(@filename) do |f|
@in = f
@scanner = StringScanner.new("")
parse
end
</syntaxhighlight>
=={{header|Tcl}}==
{{improve|Tcl|This is not an EBNF parser. It never uses EBNF. It is a calculator parser, but there is already a calculator parser at [[Arithmetic evaluation#Tcl]]. One should adjust this solution to parse the EBNF language, not the calculator language.}}
Demonstration lexer and parser. Note that this parser supports parenthesized expressions, making the grammar recursive.
<syntaxhighlight lang="tcl">package require Tcl 8.6
# Utilities to make the coroutine easier to use
Line 147 ⟶ 2,653:
}
throw SYNTAX "\"$payload\" at position $index"
}</
<
puts [parse "1 - 2 - -3 * 4 + 5"]
puts [parse "1 - 2 - -3 * (4 + 5)"]</
Output:
<pre>
PLUS {MINUS {MINUS 1 2} {MULT -3 4}} 5
MINUS {MINUS 1 2} {MULT -3 {PLUS 4 5}}
</pre>
=={{header|Wren}}==
{{trans|Phix}}
{{libheader|Wren-fmt}}
{{libheader|Wren-iterate}}
{{libheader|Wren-str}}
{{libheader|Wren-seq}}
Translated via the Go entry.
<syntaxhighlight lang="wren">import "./fmt" for Conv, Fmt
import "./iterate" for Stepped
import "./str" for Char
import "./seq" for Lst
var src = ""
var ch = ""
var sdx = 0
var token = null
var isSeq = false
var err = false
var idents = []
var ididx = []
var productions = []
var extras = []
var results = ["pass", "fail"]
var invalid = Fn.new { |msg|
err = true
System.print(msg)
sdx = src.count // set to EOF
return -1
}
var skipSpaces = Fn.new {
while (true) {
if (sdx >= src.count) return
ch = src[sdx]
if (!" \t\r\n".contains(ch)) return
sdx = sdx + 1
}
}
var getToken = Fn.new {
// Yields a single character token, one of {}()[]|=.;
// or {"terminal",string} or {"ident", string} or -1.
skipSpaces.call()
if (sdx >= src.count) {
token = -1
isSeq = false
return
}
var tokstart = sdx
if ("{}()[]|=.;".contains(ch)) {
sdx = sdx + 1
token = ch
isSeq = false
} else if (ch == "\"" || ch == "'") {
var closech = ch
for (tokend in Stepped.ascend(sdx + 1...src.count)) {
if (src[tokend] == closech) {
sdx = tokend + 1
token = ["terminal", src[tokstart+1...tokend]]
isSeq = true
return
}
}
token = invalid.call("no closing quote")
isSeq = false
} else if (Char.isAsciiLower(ch)) {
// To simplify things for the purposes of this task,
// identifiers are strictly a-z only, not A-Z or 1-9.
while (true) {
sdx = sdx + 1
if (sdx >= src.count) break
ch = src[sdx]
if (!Char.isAsciiLower(ch)) break
}
token = ["ident", src[tokstart...sdx]]
isSeq = true
} else {
token = invalid.call("invalid ebnf")
isSeq = false
}
}
var matchToken = Fn.new { |ch|
if (token != ch) {
token = invalid.call("invalid ebnf (%(ch) expected)")
isSeq = false
} else {
getToken.call()
}
}
var addIdent = Fn.new { |ident|
var k = -1
var i = 0
for (id in idents) {
if (id == ident) {
k = i
break
}
i = i + 1
}
if (k == -1) {
idents.add(ident)
k = idents.count - 1
ididx.add(-1)
}
return k
}
var expression // forward declaration
var factor = Fn.new {
var res
if (isSeq) {
if (token[0] == "ident") {
var idx = addIdent.call(token[1])
token.add(idx)
}
res = token
getToken.call()
} else if (token == "[") {
getToken.call()
res = ["optional", expression.call()]
matchToken.call("]")
} else if (token == "(") {
getToken.call()
res = expression.call()
matchToken.call(")")
} else if (token == "{") {
getToken.call()
res = ["repeat", expression.call()]
matchToken.call("}")
} else {
Fiber.abort("invalid token in factor() function")
}
if (res is Sequence && res.count == 1) return res[0]
return res
}
var term = Fn.new {
var res = [factor.call()]
var tokens = [-1, "|", ".", ";", ")", "]", "}"]
while (true) {
var outer = false
for (t in tokens) {
if (t == token) {
outer = true
break
}
}
if (outer) break
res.add(factor.call())
}
if (res.count == 1) return res[0]
return res
}
// declared earlier
expression = Fn.new {
var res = [term.call()]
if (token == "|") {
res = ["or", res[0]]
while (token == "|") {
getToken.call()
res.add(term.call())
}
}
if (res.count == 1) return res[0]
return res
}
var production = Fn.new {
// Returns a token or -1; the real result is left in 'productions' etc,
getToken.call()
if (token != "}") {
if (token == -1) return invalid.call("invalid ebnf (missing closing })")
if (!isSeq) return -1
if (token[0] != "ident") return -1
var ident = token[1]
var idx = addIdent.call(ident)
getToken.call()
matchToken.call("=")
if (token == -1) return -1
productions.add([ident, idx, expression.call()])
ididx[idx] = productions.count - 1
}
return token
}
// Adjusts Wren's normal printing of lists to look more like Phix output.
var pprint = Fn.new { |ob, header|
Fmt.print("\n$s:", header)
var quote // recursive closure
quote = Fn.new { |list|
for (i in 0...list.count) {
if (list[i] is String) {
list[i] = Fmt.swrite("$q", list[i])
} else if (list[i] is List) quote.call(list[i])
}
}
var obs
if (ob is String) {
obs = Fmt.swrite("$q", ob)
} else if (ob is List) {
obs = Lst.clone(ob)
quote.call(obs)
}
var pp = obs.toString
pp = pp.replace("[", "{")
pp = pp.replace("]", "}")
for (i in 0...idents.count) {
var xs = Fmt.swrite("'\\x$02d'", i)
pp = pp.replace(xs, i.toString)
}
System.print(pp)
}
var parse = Fn.new { |ebnf|
// Returns +1 if ok, -1 if bad.
System.print("parse:\n%(ebnf) ===>")
err = false
src = ebnf
sdx = 0
idents.clear()
ididx.clear()
productions.clear()
extras.clear()
getToken.call()
if (isSeq) {
token[0] = "title"
extras.add(token)
getToken.call()
}
if (token != "{") return invalid.call("invalid ebnf (missing opening {)")
while (true) {
token = production.call()
if (token == "}" || token == -1) break
}
getToken.call()
if (isSeq) {
token[0] = "comment"
extras.add(token)
getToken.call()
}
if (token != -1) return invalid.call("invalid ebnf (missing eof?)")
if (err) return -1
var k = -1
var i = 0
for (idx in ididx) {
if (idx == -1) {
k = i
break
}
i = i + 1
}
if (k != -1) return invalid.call("invalid ebnf (undefined:%(idents[k]))")
pprint.call(productions, "productions")
pprint.call(idents, "idents")
pprint.call(ididx, "ididx")
pprint.call(extras, "extras")
return 1
}
// The rules that applies() has to deal with are:
// {factors} - if rule[0] is not string,
// just apply one after the other recursively.
// {"terminal", "a1"} -- literal constants
// {"or", <e1>, <e2>, ...} -- (any) one of n
// {"repeat", <e1>} -- as per "{}" in ebnf
// {"optional", <e1>} -- as per "[]" in ebnf
// {"ident", <name>, idx} -- apply the sub-rule
var applies // recursive function
applies = Fn.new { |rule|
var wasSdx = sdx // in case of failure
var r1 = rule[0]
if (!(r1 is String)) {
for (i in 0...rule.count) {
if (!applies.call(rule[i])) {
sdx = wasSdx
return false
}
}
} else if (r1 == "terminal") {
skipSpaces.call()
var r2 = rule[1]
for (i in 0...r2.count) {
if (sdx >= src.count || src[sdx] != r2[i]) {
sdx = wasSdx
return false
}
sdx = sdx + 1
}
} else if (r1 == "or") {
for (i in Stepped.ascend(1...rule.count)) {
if (applies.call(rule[i])) return true
}
sdx = wasSdx
return false
} else if (r1 == "repeat") {
while (applies.call(rule[1])) {}
} else if (r1 == "optional") {
applies.call(rule[1])
} else if (r1 == "ident") {
var i = rule[2]
var ii = ididx[i]
if (!(applies.call(productions[ii][2]))) {
sdx = wasSdx
return false
}
} else {
Fiber.abort("invalid rule in applies() function")
}
return true
}
var checkValid = Fn.new { |test|
src = test
sdx = 0
var res = applies.call(productions[0][2])
skipSpaces.call()
if (sdx < src.count) res = false
Fmt.print("$q, $s", test, results[1-Conv.btoi(res)])
}
var ebnfs = [
""""a" {
a = "a1" ( "a2" | "a3" ) { "a4" } [ "a5" ] "a6" ;
} "z" """,
"""{
expr = term { plus term } .
term = factor { times factor } .
factor = number | '(' expr ')' .
plus = "+" | "-" .
times = "*" | "/" .
number = digit { digit } .
digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" .
}""",
"a = \"1\"",
"""{ a = "1" ;""",
"""{ hello world = "1"; }""",
"""{ foo = bar . }"""
]
var tests = [
[
"a1a3a4a4a5a6",
"a1 a2a6",
"a1 a3 a4 a6",
"a1 a4 a5 a6",
"a1 a2 a4 a5 a5 a6",
"a1 a2 a4 a5 a6 a7",
"your ad here"
],
[
"2",
"2*3 + 4/23 - 7",
"(3 + 4) * 6-2+(4*(4))",
"-2",
"3 +",
"(4 + 3"
]
]
var i = 0
for (ebnf in ebnfs) {
if (parse.call(ebnf) == 1) {
System.print("\ntests:")
for (test in tests[i]) checkValid.call(test)
}
System.print()
i = i + 1
}</syntaxhighlight>
{{out}}
<pre>
parse:
"a" {
a = "a1" ( "a2" | "a3" ) { "a4" } [ "a5" ] "a6" ;
} "z" ===>
productions:
{{"a", 0, {{"terminal", "a1"}, {"or", {"terminal", "a2"}, {"terminal", "a3"}}, {"repeat", {"terminal", "a4"}}, {"optional", {"terminal", "a5"}}, {"terminal", "a6"}}}}
idents:
{"a"}
ididx:
{0}
extras:
{{"title", "a"}, {"comment", "z"}}
tests:
"a1a3a4a4a5a6", pass
"a1 a2a6", pass
"a1 a3 a4 a6", pass
"a1 a4 a5 a6", fail
"a1 a2 a4 a5 a5 a6", fail
"a1 a2 a4 a5 a6 a7", fail
"your ad here", fail
parse:
{
expr = term { plus term } .
term = factor { times factor } .
factor = number | '(' expr ')' .
plus = "+" | "-" .
times = "*" | "/" .
number = digit { digit } .
digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" .
} ===>
productions:
{{"expr", 0, {{"ident", "term", 1}, {"repeat", {{"ident", "plus", 2}, {"ident", "term", 1}}}}}, {"term", 1, {{"ident", "factor", 3}, {"repeat", {{"ident", "times", 4}, {"ident", "factor", 3}}}}}, {"factor", 3, {"or", {"ident", "number", 5}, {{"terminal", "("}, {"ident", "expr", 0}, {"terminal", ")"}}}}, {"plus", 2, {"or", {"terminal", "+"}, {"terminal", "-"}}}, {"times", 4, {"or", {"terminal", "*"}, {"terminal", "/"}}}, {"number", 5, {{"ident", "digit", 6}, {"repeat", {"ident", "digit", 6}}}}, {"digit", 6, {"or", {"terminal", "0"}, {"terminal", "1"}, {"terminal", "2"}, {"terminal", "3"}, {"terminal", "4"}, {"terminal", "5"}, {"terminal", "6"}, {"terminal", "7"}, {"terminal", "8"}, {"terminal", "9"}}}}
idents:
{"expr", "term", "plus", "factor", "times", "number", "digit"}
ididx:
{0, 1, 3, 2, 4, 5, 6}
extras:
{}
tests:
"2", pass
"2*3 + 4/23 - 7", pass
"(3 + 4) * 6-2+(4*(4))", pass
"-2", fail
"3 +", fail
"(4 + 3", fail
parse:
a = "1" ===>
invalid ebnf (missing opening {)
parse:
{ a = "1" ; ===>
invalid ebnf (missing closing })
parse:
{ hello world = "1"; } ===>
invalid ebnf (= expected)
parse:
{ foo = bar . } ===>
invalid ebnf (undefined:bar)
</pre>
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