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Here is an CGI calculator script, cgicalc.scm, that
exploits Scheme's arbitrary-precision arithmetic.
#!/bin/sh
":";exec /usr/local/bin/mzscheme -r $0
;Load the CGI utilities
(load-relative "cgi.scm")
(define uhoh #f)
(define calc-eval
(lambda (e)
(if (pair? e)
(apply (ensure-operator (car e))
(map calc-eval (cdr e)))
(ensure-number e))))
(define ensure-operator
(lambda (e)
(case e
((+) +)
((-) -)
((*) *)
((/) /)
((**) expt)
(else (uhoh "unpermitted operator")))))
(define ensure-number
(lambda (e)
(if (number? e) e
(uhoh "non-number"))))
(define print-form
(lambda ()
(display "<form action=\"")
(display (getenv "SCRIPT_NAME"))
(display "\">
Enter arithmetic expression:<br>
<input type=textarea name=arithexp><p>
<input type=submit value=\"Evaluate\">
<input type=reset value=\"Clear\">
</form>")))
(define print-page-begin
(lambda ()
(display "content-type: text/html
<html>
<head>
<title>A Scheme Calculator</title>
</head>
<body>")))
(define print-page-end
(lambda ()
(display "</body>
</html>")))
(parse-form-data)
(print-page-begin)
(let ((e (form-data-get "arithexp")))
(unless (null? e)
(let ((e1 (car e)))
(display-html e1)
(display "<p>
=> ")
(display-html
(call/cc
(lambda (k)
(set! uhoh
(lambda (s)
(k (string-append "Error: " s))))
(number->string
(calc-eval (read (open-input-string (car e))))))))
(display "<p>"))))
(print-form)
(print-page-end)
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