;;; input.ss
;;;   A library of routines for getting input from the user.
;;; Author:
;;;   Samuel A. Rebelsky
;;; Version:
;;;   1.1 of October 2000
;;; Contents:
;;;   Input Routines
;;;   Helper Routines

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;;; Input Routines

;;; Read a positive number from the standard input port.
;;; Parameters:
;;;   A prompt
;;; Preconditions:
;;;   The standard input port is available for reading.
;;; Postconditions:
;;;   Reads some input.
;;;   Writes some output (particularly the prompt).
;;; Returns:
;;;   A positive number.
(define read-positive-number
  (lambda (prompt)
    (display prompt)
    (let ((val (read)))
      (if (number? val) val
          (begin (display "That is not a number.  ")
                 (newline)
                 (read-positive-number))))))
                 
;;; Read a string from the standard input port.  If the user enters
;;; something other than a string, try to treat it as a string.
;;; Parameters:
;;;   A prompt.
;;; Preconditions:
;;;   The standard input port is available for reading.
;;; Postconditions:
;;;   Reads some input.
;;;   Writes some output.
;;; Returns:
;;;   A string.
(define read-string
  (lambda (prompt)
    (display prompt)
    (make-string (read))))
    
;;; Read one of a list of symbols.  If the user enters something
;;; other than one of the valid symbols, tries again.
;;; Parameters:
;;;   A non-empty list of valid symbols.
;;; Preconditions:
;;;   The list is not empty.
;;;   The list contains only symbols.
;;;   The standard input port is available for reading.
;;; Postconditions:
;;;   Reads some input.
;;;   Writes some output.
;;; Returns:
;;;     One of the symbols in the list (as specified by
;;;     the user).
;;;   
(define read-symbol
  (lambda (prompt valid)
    (display prompt)
    (display valid)
    (display " ")
    (let ((sym (read)))
      (if (member sym valid) sym
          (begin
            (display sym)
            (display " is not a valid response. ")
            (newline)
            (read-symbol prompt valid))))))

;;; Read a list of strings.  
;;; Parameters:
;;;   A prompt.
;;;   A string that terminates input.
;;; Preconditions:
;;;   Both parameters are strings.
;;;   The standard input port is available for reading.
;;; Postconditions:
;;;   Reads some input.
;;;   Writes some output (particularly the prompt).
(define read-string-list
  (lambda (prompt terminator)
    (let ((val (read-string prompt)))
      (if (equal? val terminator) null
          (cons val (read-string-list prompt terminator))))))

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;;; Other utilities

;;; Turn something read into a string (because the typical input is
;;; a symbol rather than a string).
;;; Parameters:
;;;   A number, string, or symbol.
;;; Preconditions:
;;;   The paremeter is a number, string, or symbol.
;;; Postconditions:
;;;   Returns the string equivalent of the parameter.
;;;   Does not affect the parameter.
(define make-string
  (lambda (stuff)
    (cond
      ((string? stuff) stuff)
      ((symbol? stuff) (symbol->string stuff))
      ((number? stuff) (number->string stuff))
      (else "*UNKNOWN*"))))

;;; Capitalize the first letter of a string.
;;; Parameters:
;;;   A string
;;; Precondition:
;;;   The string is nonempty and contains no spaces.
;;; Postcondition:
;;;   Returns the stame string with the first letter capitalized.
(define capfirst
  (lambda (str)
    (let ((firstchar (string-ref str 0))
          (rest (substring str 1 (string-length str))))
      (string-append (string (char-upcase firstchar)) rest))))