Compiler/Verifying syntax: Difference between revisions
→{{header|Go}}: Further tweaks and examples.
(→{{header|Go}}: Further tweaks and examples.) |
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After making the appropriate substitutions, we can therefore use the parser in Go's standard library to verify whether the statements are valid or not. As expressions cannot be statements in Go, we simply parse the latter as expressions.
However, before applying the parser, we first need to ensure that the expressions don't include any characters (including non-ASCII) or usages thereof which Go would otherwise permit. Note that it's not necessary to specifically check for
In particular, after substitutions,
<lang go>package main
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var (
re1 = regexp.MustCompile(`[^_a-zA-Z0-9\+\-\*/=<\(\)
re2 = regexp.MustCompile(`\b_\w*\b`)
re3 = regexp.MustCompile(`
re4 = regexp.MustCompile(`(=|<)
)
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matches = re4.FindStringSubmatch(expr)
if matches != nil {
return fmt.Errorf("
}
return nil
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func main() {
exprs := []string{
"3 + not 5",
"3 + (not 5)",
"(42 + 3",
" not 3 < 4 or (true or 3 / 4 + 8 * 5 - 5 * 2 < 56) and 4 * 3 < 12 or not true",
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"not 7 < 2",
"2 < 3 < 4",
"2 < foobar - 3 < 4",
"2 < foobar and 3 < 4",
"4 * (32 - 16) + 9 = 73",
"235 76 + 1",
"a + b = not c and false",
"a + b = (not c) and false",
"a + b = (not c and false)",
"ab_c / bd2 or < e_f7",
"g not = h",
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{{out}}
<pre>
Statement to verify: "3 + not 5"
"false" -> expected operand, found 'not'
Statement to verify: "3 + (not 5)"
"true"
Statement to verify: "(42 + 3"
"false" -> expected ')', found newline
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Statement to verify: "2 < 3 < 4"
"false" ->
Statement to verify: "2 < foobar - 3 < 4"
"false" -> operator '<' is non-associative
Statement to verify: "2 < foobar and 3 < 4"
"true"
Statement to verify: "4 * (32 - 16) + 9 = 73"
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Statement to verify: "a + b = (not c) and false"
"true"
Statement to verify: "a + b = (not c and false)"
"true"
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