106 lines
3.1 KiB
Scheme
106 lines
3.1 KiB
Scheme
(define-structure servlet servlet-interface
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(open servlets
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httpd-requests
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handle-fatal-error
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let-opt
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scheme-with-scsh)
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(begin
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;; This uses callbacks.
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(define *operator-alist*
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`(("+" . ,+)
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("-" . ,-)
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("*" . ,*)
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("/" . ,/)))
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(define operator-symbol car)
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(define operator-operator cdr)
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(define operator-input-field
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(let ((name (generate-input-field-name "operator")))
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(make-input-field
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name
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(lambda (operator-string)
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(cond
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((assoc operator-string *operator-alist*) =>
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(lambda (a) a))
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(else
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(error "no such operator" operator-string))))
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`(select (@ (name ,name))
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,@(map (lambda (operator)
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`(option ,(operator-symbol operator)))
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*operator-alist*)))))
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(define (change-operator-callback)
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(make-callback
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(lambda (req)
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(change-operator
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;; This yields an error only when the browser is doing wrong.
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(input-field-value operator-input-field
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(get-bindings req))))
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))
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(define (make-number-input-field/default default)
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(if default
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(make-number-input-field `(@ (value ,default)))
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(make-number-input-field)))
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(define (show-page operator-pair number1 number2 . maybe-update-text)
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(let* ((update-text (:optional maybe-update-text ""))
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(number-field1 (make-number-input-field/default number1))
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(number-field2 (make-number-input-field/default number2))
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(req
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(send-html/suspend
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(lambda (new-url)
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`(html
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(title "Simple calculator")
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(body (h1 "Simple calculator")
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(font (@ (color "red")) ,update-text)
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(servlet-form
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,new-url
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(table
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(tr (td "Do calculation:"))
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(tr (td ,number-field1)
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(td ,(operator-symbol operator-pair))
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(td ,number-field2)
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(td " = ")
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(td ,(make-submit-button '(@ (value "calculate")))))))
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(hr)
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(p "You may choose another operator:")
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(servlet-form
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,(change-operator-callback)
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(table
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(tr (td ,operator-input-field)
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(td ,(make-submit-button
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'(@ (value "change operator"))))))))))))
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(bindings (get-bindings req)))
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(let ((number1 (input-field-value number-field1 bindings))
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(number2 (input-field-value number-field2 bindings)))
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(if number1
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(if number2
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(calculate operator-pair number1 number2)
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(show-page operator-pair number1 number2 "Please enter a valid second number."))
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(show-page operator-pair number1 number2 "Please enter a valid first number."))
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)))
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(define (change-operator to-operation)
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(show-page to-operation #f #f))
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(define (calculate operator-pair number1 number2)
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(let ((operator (operator-operator operator-pair)))
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(show-result number1 (operator-symbol operator-pair) number2
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(operator number1 number2))))
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(define (show-result number1 operator-symbol number2 result)
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(send-html
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`(html (title "Calculation Result")
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(body (h1 "Result")
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(p ,number1 " " ,operator-symbol " " ,number2
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" = " ,result)))))
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(define (main req)
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(show-page (car *operator-alist*) #f #f)
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(error "This does not return"))
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)) |