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90 lines
2.6 KiB
Racket
90 lines
2.6 KiB
Racket
#lang scheme
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;; An interactive calculator inspired by the calculator example in the bison manual.
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;; Import the parser and lexer generators.
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(require parser-tools/yacc
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parser-tools/lex
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(prefix-in : parser-tools/lex-sre))
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(define-tokens value-tokens (NUM VAR FNCT))
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(define-empty-tokens op-tokens (newline = OP CP + - * / ^ EOF NEG))
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;; A hash table to store variable values in for the calculator
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(define vars (make-hash))
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(define-lex-abbrevs
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(lower-letter (:/ "a" "z"))
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(upper-letter (:/ #\A #\Z))
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;; (:/ 0 9) would not work because the lexer does not understand numbers. (:/ #\0 #\9) is ok too.
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(digit (:/ "0" "9")))
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(define calcl
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(lexer
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[(eof) 'EOF]
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;; recursively call the lexer on the remaining input after a tab or space. Returning the
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;; result of that operation. This effectively skips all whitespace.
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[(:or #\tab #\space) (calcl input-port)]
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;; (token-newline) returns 'newline
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[#\newline (token-newline)]
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;; Since (token-=) returns '=, just return the symbol directly
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[(:or "=" "+" "-" "*" "/" "^") (string->symbol lexeme)]
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["(" 'OP]
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[")" 'CP]
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["sin" (token-FNCT sin)]
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[(:+ (:or lower-letter upper-letter)) (token-VAR (string->symbol lexeme))]
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[(:+ digit) (token-NUM (string->number lexeme))]
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[(:: (:+ digit) #\. (:* digit)) (token-NUM (string->number lexeme))]))
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(define calcp
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(parser
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(start start)
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(end newline EOF)
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(tokens value-tokens op-tokens)
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(error (lambda (a b c) (void)))
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(precs (right =)
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(left - +)
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(left * /)
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(left NEG)
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(right ^))
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(grammar
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(start [() #f]
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;; If there is an error, ignore everything before the error
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;; and try to start over right after the error
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[(error start) $2]
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[(exp) $1])
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(exp [(NUM) $1]
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[(VAR) (hash-ref vars $1 (lambda () 0))]
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[(VAR = exp) (begin (hash-set! vars $1 $3)
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$3)]
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[(FNCT OP exp CP) ($1 $3)]
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[(exp + exp) (+ $1 $3)]
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[(exp - exp) (- $1 $3)]
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[(exp * exp) (* $1 $3)]
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[(exp / exp) (/ $1 $3)]
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[(- exp) (prec NEG) (- $2)]
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[(exp ^ exp) (expt $1 $3)]
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[(OP exp CP) $2]))))
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;; run the calculator on the given input-port
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(define (calc ip)
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(port-count-lines! ip)
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(letrec ((one-line
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(lambda ()
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(let ((result (calcp (lambda () (calcl ip)))))
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(when result
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(printf "~a\n" result)
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(one-line))))))
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(one-line)))
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(calc (open-input-string "x=1\n(x + 2 * 3) - (1+2)*3"))
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