functions.scm

;;; The functions program

;;; Copyright (C) 1993 by Matthew Wright and Brian Harvey

;;;     This program is free software; you can redistribute it and/or modify
;;;     it under the terms of the GNU General Public License as published by
;;;     the Free Software Foundation; either version 2 of the License, or
;;;     (at your option) any later version.
;;; 
;;;     This program is distributed in the hope that it will be useful,
;;;     but WITHOUT ANY WARRANTY; without even the implied warranty of
;;;     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;;;     GNU General Public License for more details.
;;; 
;;;     You should have received a copy of the GNU General Public License
;;;     along with this program; if not, write to the Free Software
;;;     Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.


(define (functions)
  (read-line)
  (show "Welcome to the FUNCTIONS program.")
  (functions-loop))

(define (functions-loop)
  (let ((fn-name (get-fn)))
    (if (equal? fn-name 'exit)
	"Thanks for using FUNCTIONS!"
	(let ((args (get-args (arg-count fn-name))))
	  (if (not (in-domain? args fn-name))
	     (show "Argument(s) not in domain.")
	     (show-answer (apply (scheme-function fn-name) args)))
	  (functions-loop)))))

(define (get-fn)
  (display "Function: ")
  (let ((line (read-line)))
    (cond ((empty? line)
	   (show "Please type a function!")
	   (get-fn))
	  ((not (= (count line) 1))
	   (show "You typed more than one thing!  Try again.")
	   (get-fn))
	  ((not (valid-fn-name? (first line)))
	   (show "Sorry, that's not a function.")
	   (get-fn))
	  (else (first line)))))

(define (get-args n)
  (if (= n 0)
      '()
      (let ((first (get-arg)))
	(cons first (get-args (- n 1))))))

(define (get-arg)
  (display "Argument: ")
  (let ((line (read-line)))
    (cond ((empty? line)
	   (show "Please type an argument!")
	   (get-arg))
	  ((and (equal? "(" (first (first line)))
		(equal? ")" (last (last line))))
	   (let ((sent (remove-first-paren (remove-last-paren line))))
	     (if (any-parens? sent)
		 (begin
		  (show "Sentences can't have parentheses inside.")
		  (get-arg))
		 (map booleanize sent))))
	  ((any-parens? line)
	   (show "Bad parentheses")
	   (get-arg))
	  ((empty? (bf line)) (booleanize (first line)))
	  (else (show "You typed more than one argument!  Try again.")
		(get-arg)))))

(define (any-parens? line)
  (let ((letters (accumulate word line)))
    (or (member? "(" letters)
	(member? ")" letters))))

(define (remove-first-paren line)
  (if (equal? (first line) "(")
      (bf line)
      (se (bf (first line)) (bf line))))

(define (remove-last-paren line)
  (if (equal? (last line) ")")
      (bl line)
      (se (bl line) (bl (last line)))))

(define (booleanize x)
  (cond ((equal? x "#t") #t)
	((equal? x "#f") #f)
	(else x)))

(define (show-answer answer)
  (newline)
  (display "The result is: ")
  (if (not answer)
      (show "#F")
      (show answer))
  (newline))

(define (scheme-function fn-name)
  (cadr (assoc fn-name *the-functions*)))

(define (arg-count fn-name)
  (caddr (assoc fn-name *the-functions*)))

(define (type-predicate fn-name)
  (cadddr (assoc fn-name *the-functions*)))

(define (in-domain? args fn-name)
  (apply (type-predicate fn-name) args))


;; Type predicates

(define (word-or-sent? x)
  (or (word? x) (sentence? x)))

(define (not-empty? x)
  (and (word-or-sent? x) (not (empty? x))))

(define (two-numbers? x y)
  (and (number? x) (number? y)))

(define (two-reals? x y)
  (and (real? x) (real? y)))

(define (two-integers? x y)
  (and (integer? x) (integer? y)))

(define (can-divide? x y)
  (and (number? x) (number? y) (not (= y 0))))

(define (dividable-integers? x y)
  (and (two-integers? x y) (not (= y 0))))

(define (trig-range? x)
  (and (number? x) (<= (abs x) 1)))

(define (hof-types-ok? fn-name stuff range-predicate)
  (and (valid-fn-name? fn-name)
       (= 1 (arg-count fn-name))
       (word-or-sent? stuff)
       (empty? (keep (lambda (element)
		       (not ((type-predicate fn-name) element)))
		     stuff))
       (null? (filter (lambda (element)
			(not (range-predicate element)))
		      (map (scheme-function fn-name)
			   (every (lambda (x) x) stuff))))))

(define (member-types-ok? small big)
  (and (word? small)
       (or (sentence? big) (= (count small) 1))))


;; Names of functions as functions

(define (named-every fn-name list)
  (every (scheme-function fn-name) list))

(define (named-keep fn-name list)
  (keep (scheme-function fn-name) list))

(define (valid-fn-name? name)
  (assoc name *the-functions*))


;; The list itself
          
(define *the-functions*
  (list (list '* * 2 two-numbers?)
	(list '+ + 2 two-numbers?)
	(list '- - 2 two-numbers?)
	(list '/ / 2 can-divide?)
	(list '< < 2 two-reals?)
	(list '<= <= 2 two-reals?)
	(list '= = 2 two-numbers?)
	(list '> > 2 two-reals?)
	(list '>= >= 2 two-reals?)
	(list 'abs abs 1 real?)

	(list 'acos acos 1 trig-range?)
	(list 'and (lambda (x y) (and x y)) 2 
	      (lambda (x y) (and (boolean? x) (boolean? y))))
	(list 'appearances appearances 2 member-types-ok?)
	(list 'asin asin 1 trig-range?)
	(list 'atan atan 1 number?)
	(list 'bf bf 1 not-empty?)
	(list 'bl bl 1 not-empty?)
	(list 'butfirst butfirst 1 not-empty?)
	(list 'butlast butlast 1 not-empty?)
	(list 'ceiling ceiling 1 real?)
	(list 'cos cos 1 number?)
	(list 'count count 1 word-or-sent?)
	(list 'equal? equal? 2 (lambda (x y) #t))
	(list 'even? even? 1 integer?)
	(list 'every named-every 2
	      (lambda (fn stuff)
		(hof-types-ok? fn stuff word-or-sent?)))
	(list 'exit '() 0 '())
	   ; in case user applies number-of-arguments to exit
	(list 'exp exp 1 number?)
	(list 'expt expt 2
	      (lambda (x y)
		(and (number? x) (number? y)
		     (or (not (real? x)) (>= x 0) (integer? y)))))
	(list 'first first 1 not-empty?)
	(list 'floor floor 1 real?)
	(list 'gcd gcd 2 two-integers?)
	(list 'if (lambda (pred yes no) (if pred yes no)) 3
	      (lambda (pred yes no) (boolean? pred)))
	(list 'item item 2
	      (lambda (n stuff)
		(and (integer? n) (> n 0)
		     (word-or-sent? stuff) (<= n (count stuff)))))
	(list 'keep named-keep 2
	      (lambda (fn stuff)
		(hof-types-ok? fn stuff boolean?)))
	(list 'last last 1 not-empty?)
	(list 'lcm lcm 2 two-integers?)
	(list 'log log 1 (lambda (x) (and (number? x) (not (= x 0)))))
	(list 'max max 2 two-reals?)
	(list 'member? member? 2 member-types-ok?)
	(list 'min min 2 two-reals?)
	(list 'modulo modulo 2 dividable-integers?)
	(list 'not not 1 boolean?)
	(list 'number? number? 1 (lambda (x) #t))
	(list 'number-of-arguments arg-count 1 valid-fn-name?)

	(list 'odd? odd? 1 integer?)
	(list 'or (lambda (x y) (or x y)) 2
	      (lambda (x y) (and (boolean? x) (boolean? y))))
	(list 'quotient quotient 2 dividable-integers?)
	(list 'random random 1 (lambda (x) (and (integer? x) (> x 0))))
	(list 'remainder remainder 2 dividable-integers?)
	(list 'round round 1 real?)
	(list 'se se 2
	      (lambda (x y) (and (word-or-sent? x) (word-or-sent? y))))
	(list 'sentence sentence 2
	      (lambda (x y) (and (word-or-sent? x) (word-or-sent? y))))
	(list 'sentence? sentence? 1 (lambda (x) #t))
	(list 'sin sin 1 number?)
	(list 'sqrt sqrt 1 (lambda (x) (and (real? x) (>= x 0))))
	(list 'tan tan 1 number?)
	(list 'truncate truncate 1 real?)
	(list 'vowel? (lambda (x) (member? x '(a e i o u))) 1
	      (lambda (x) #t))
	(list 'word word 2 (lambda (x y) (and (word? x) (word? y))))
	(list 'word? word? 1 (lambda (x) #t))))