75 lines
2.1 KiB
Racket
75 lines
2.1 KiB
Racket
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#lang racket
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;; (C) Copyright Collin J. Doering 2014
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;;
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;; This program is free software: you can redistribute it and/or modify
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;; it under the terms of the GNU General Public License as published by
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;; the Free Software Foundation, either version 3 of the License, or
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;; (at your option) any later version.
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;;
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;; This program is distributed in the hope that it will be useful,
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;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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;; GNU General Public License for more details.
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;;
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;; You should have received a copy of the GNU General Public License
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;; along with this program. If not, see <http://www.gnu.org/licenses/>.
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;; File: church-booleans.rkt
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;; Author: Collin J. Doering <collin.doering@rekahsoft.ca>
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;; Date: Oct 28, 2014
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;; Implementation of booleans with only the use of define and lambda
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(define my-true (lambda (x)
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(lambda (y) x)))
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(define my-false (lambda (x)
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(lambda (y) y)))
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(define (to-built-in-bool a)
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((a #t) #f))
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(define (not a)
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(lambda (x)
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(lambda (y)
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(((a) y) x))))
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(define (and-op a b)
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(let ([evaled-a (a)])
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((evaled-a (b)) evaled-a)))
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(define (my-and . xs)
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(foldr and-op my-true xs))
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(define (or-op a b)
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(let ([evaled-a (a)])
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((evaled-a evaled-a) (b))))
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(define (my-or . xs)
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(foldr or-op my-false xs))
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;; (lazy-fun (f x1 ... xn) body) => macro with name "f-lazy" generated which is like the lazy-funcall macro
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;; (lazy-funcall f x1 ... xn) ==> (f (lambda () x1) ... (lambda () xn))
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;;
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;; Testing the functions
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;;
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(displayln "Testing and: should output false then #f on the next line indicating and (as well as and-op) did not evaluate its second argument")
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(to-built-in-bool
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(my-and
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(begin (displayln 'false)
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my-false)
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(begin (displayln 'what)
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my-true)))
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(newline)
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(displayln "Testing or: should output true then #t on the next line indicating or (and or-op) did not evaluate its second argument")
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(to-built-in-bool
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(my-or
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(begin (displayln 'true)
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my-true)
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(begin (displayln 'what)
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my-false)))
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