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96 lines
3.2 KiB
Scheme
96 lines
3.2 KiB
Scheme
;; 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 (lib "yacc.ss" "parser-tools")
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(lib "lex.ss" "parser-tools")
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(lib "readerr.ss" "syntax"))
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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-table))
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(define-lex-abbrevs
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(lower-letter (- a z))
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;; In the following line if we used (- A Z) dr/mzscheme would read it as (- a z) if
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;; case-sensitivity is not enabled. (- #\A #\Z) will not be altered because dr/mzscheme
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;; reads them as character constants and not as symbols. (- "A" "Z") would work as well
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;; since dr/mzscheme would read them as strings. The lexer generator treates single character
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;; strings and symbols the same as an actual #\ character. #cs(- A Z) works too because the #cs
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;; tells dr/mzscheme to read the next expression with case-sensitivity turned on.
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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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[(: #\tab #\space) (calcl input-port)]
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;; The parser will treat the return of 'newline the same as (token-newline)
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[#\newline 'newline]
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[(: = + - * / ^) (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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;; It the parens are left off of an "invocation" of an abbreviation, it means the
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;; character sequence instead.
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[(+ (: (lower-letter) (upper-letter))) (token-VAR (string->symbol lexeme))]
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[(+ (digit)) (token-NUM (string->number lexeme))]
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;; Strings which dr/mzscheme does not think of as symbols (such as . or ,) must be
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;; entered as a string or character. "." would also be ok.
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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-table-get vars $1 (lambda () 0))]
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[(VAR = exp) (begin (hash-table-put! 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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(if result
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(begin
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(printf "~a~n" result)
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(one-line)))))))
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(one-line)))
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