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Arithmetic evaluation: Difference between revisions
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→{{header|D}}: AST is built & remove incorrect tag
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=={{header|D}}==
Following the previous number-operator dual stacks approach, an AST is built while previous version is evaluating the expression value. After the AST tree is constructed, a visitor pattern is used to display the AST structure and calculate the value.
<
import std.stdio, std.string, std.ctype, std.conv ;
// simple stack template
void push(
T pop(T)(inout T[] stk,
T top ;
if (stk.length == 0) throw new Exception("Stack Empty") ;
top = stk[$-1] ;
if (discard) stk.length = stk.length - 1 ;
return top ;
}
alias int Type ;
enum { Num, OBkt, CBkt, Add, Sub, Mul, Div } ; // Type
string[] opChar = ["#","(",")","+","-","*","/"] ;
int[]
abstract class Visitor { void visit(XP e) ; }
class XP {
string str ;
int pos ; // optional, for dispalying AST struct.
XP LHS, RHS = null ;
this(string s = ")", int p = -1) {
str = s ; pos = p ;
type = Num ;
for(Type t = Div ; t > Num ; t--)
if(opChar[t] == s) type = t ;
}
int opCmp(XP rhs) { return opPrec[type] - opPrec[rhs.type] ; }
void accept(Visitor v) { v.visit(this) ; } ;
}
class AST {
XP root ;
XP[] num, opr ;
string
int xpHead, xpTail ;
void joinXP(XP x) { x.RHS = num.pop() ; x.LHS = num.pop() ; num.push(x) ; }
string nextToken() {
while (xpHead < xpr.length && xpr[xpHead] == ' ')
xpHead++ ; // skip spc
token = xpr[xpTail..xpTail+1] ;
switch(token) {
case "(",")","+","-","*","/":
default: // should be number
if(isdigit(token[0])) {
while(xpTail < xpr.length && isdigit(xpr[xpTail]))
xpTail++ ;
return xpr[xpHead..xpTail] ;
} // else may be error
} // end switch
}
if(xpTail < xpr.length)
throw new Exception("Invalid Char <" ~ xpr[xpTail] ~ ">") ;
return null ;
} // end nextToken
AST parse(string s) {
bool expectingOP ;
xpr = s ;
try {
xpHead = xpTail = 0 ;
num = opr = null ;
root = null ;
opr.push(new XP) ; // CBkt, prevent evaluate null OP precidence
while((token = nextToken) !is null) {
XP tokenXP = new XP(token, xpHead) ;
if(expectingOP) { // process OP-alike XP
switch(token) {
case ")":
while(opr.pop(false).type != OBkt)
joinXP(opr.pop()) ;
opr.pop() ;
expectingOP = true ; break ;
case "+","-","*","/":
while (tokenXP <= opr.pop(false))
joinXP(opr.pop()) ;
opr.push(tokenXP) ;
expectingOP = false ; break ;
default:
throw new Exception("Expecting Operator or ), not <" ~ token ~ ">") ;
}
} else { // process Num-alike XP
switch(token) {
case "+","-","*","/",")":
throw new Exception("Expecting Number or (, not <" ~ token ~ ">") ;
case "(":
opr.push(tokenXP) ;
expectingOP = false ; break ;
default: // number
num.push(tokenXP) ;
expectingOP = true ;
}
}
xpHead = xpTail ;
} // end while
while (opr.length > 1) // join pending Op
joinXP(opr.pop()) ;
}catch(Exception e) {
writefln("%s\n%s\n%s^", e.msg, xpr, repeat(" ", xpHead)) ;
root = null ;
return this ;
}
if(num.length != 1) { // should be one XP left
writefln("Parse Error...") ;
root = null ;
} else
root = num.pop() ;
return this ;
} // end Parse
} // end class AST
// for display AST fancy struct
void ins(inout char[][] s, string v, int p, int l) {
while(s.length < l + 1) s.length = s.length + 1 ;
while(s[l].length < p + v.length + 1) s[l] ~= " " ;
s[l][p..p +v.length] = v ;
}
class calcVis : Visitor {
int result, level = 0 ;
string Result = null ;
char[][] Tree = null ;
static void opCall(AST a) {
if (a && a.root) {
calcVis c = new calcVis ;
a.root.accept(c) ;
for(int i = 1; i < c.Tree.length ; i++) { // more fancy
bool flipflop = false ; char mk = '.' ;
for(int j = 0 ; j < c.Tree[i].length ; j++) {
while(j >= c.Tree[i-1].length) c.Tree[i-1] ~= " " ;
char c1 = c.Tree[i][j] ; char c2 = c.Tree[i-1][j] ;
if(flipflop && (c1 == ' ') && c2 == ' ')
c.Tree[i-1][j] = mk ;
if(c1 != mk && c1 != ' ' && (j == 0 || !isdigit(c.Tree[i][j-1])))
flipflop = !flipflop ;
}
}
foreach(t; c.Tree) writefln(t) ;
writefln("%s ==>\n%s = %s", a.xpr,c.Result,c.result) ;
} else
writefln("Evalute invalid or null Expression") ;
}
void visit(XP xp) {// calc. the value, display AST struct and eval order.
ins(Tree, xp.str, xp.pos, level) ;
level++ ;
if (xp.type == Num) {
Result ~= xp.str ;
result = toInt(xp.str) ;
} else {
Result ~= "(" ;
xp.LHS.accept(this) ;
int lhs = result ;
Result ~= opChar[xp.type] ;
xp.RHS.accept(this) ;
Result ~= ")" ;
switch(xp.type) {
case Add: result = lhs + result ; break ;
case Sub: result = lhs - result ; break ;
case Mul: result = lhs * result ; break ;
case Div: result = lhs / result ; break ;
default: throw new Exception("Invalid type") ;
}
} //
level-- ;
}
}
void main(string[] args) {
"1 + 2*(3 - 2*(3 - 2)*((2 - 4)*5 - 22/(7 + 2*(3 - 1)) - 1)) + 1" ; // should be 60
calcVis((new AST).parse(expression)) ;
}</d>
=={{header|Haskell}}==
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