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Arithmetic evaluation: Difference between revisions
→{{header|Racket}}
m (Fixed Julia) |
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Line 3,279:
>>> eval(code_object)
16</lang>
=={{header|Racket}}==
<lang Racket>
#lang racket
(require parser-tools/yacc parser-tools/lex
(prefix-in ~ parser-tools/lex-sre))
(define-tokens value-tokens (NUM))
(define-empty-tokens op-tokens (OPEN CLOSE + - * / EOF NEG))
(define lex
(lexer [(eof) 'EOF]
[whitespace (lex input-port)]
[(~or "+" "-" "*" "/") (string->symbol lexeme)]
["(" 'OPEN]
[")" 'CLOSE]
[(~: (~+ numeric) (~? #\. (~* numeric)))
(token-NUM (string->number lexeme))]))
(define parse
(parser [start E] [end EOF]
[tokens value-tokens op-tokens]
[error void]
[precs (left - +) (left * /) (left NEG)]
[grammar (E [(NUM) $1]
[(E + E) (+ $1 $3)]
[(E - E) (- $1 $3)]
[(E * E) (* $1 $3)]
[(E / E) (/ $1 $3)]
[(- E) (prec NEG) (- $2)]
[(OPEN E CLOSE) $2])]))
(define (calc str)
(define i (open-input-string str))
(displayln (parse ( () (lex i)))))
(calc "(1 + 2 * 3) - (1+2)*-3")
</lang>
=={{header|REXX}}==
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