53 lines
1.9 KiB
Common Lisp
53 lines
1.9 KiB
Common Lisp
;;; Copyright 2013 Google Inc.
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;;;
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;;; Licensed under the Apache License, Version 2.0 (the "License");
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;;; you may not use this file except in compliance with the License.
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;;; You may obtain a copy of the License at
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;;;
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;;; http://www.apache.org/licenses/LICENSE-2.0
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;;;
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;;; Unless required by applicable law or agreed to in writing, software
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;;; distributed under the License is distributed on an "AS IS" BASIS,
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;;; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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;;; See the License for the specific language governing permissions and
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;;; limitations under the License.
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(define-test t-and-nil-are-opposites
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;; NOT is a function which returns the boolean opposite of its argument.
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(true-or-false? t (not nil))
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(true-or-false? nil (not t)))
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(define-test nil-and-empty-list-are-the-same-thing
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;; In Common Lisp, NIL is also the empty list.
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(true-or-false? NIL '())
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(true-or-false? t (not '())))
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(define-test in-lisp-many-things-are-true
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;; In Common Lisp, the canonical values for truth is T.
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;; However, everything that is non-NIL is true, too.
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(true-or-false? t 5)
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(true-or-false? nil (not 5))
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(true-or-false? t "a string")
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;; Even an empty string...
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(true-or-false? t "")
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;; ...or a list containing a NIL...
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(true-or-false? t (list nil))
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;; ...or an array with no elements...
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(true-or-false? t (make-array 0))
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;; ...or the number zero.
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(true-or-false? t 0))
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(define-test and
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;; The logical operator AND can take multiple arguments.
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(true-or-false? t (and t t t t t))
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(true-or-false? nil (and t t nil t t))
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;; If all values passed to AND are true, it returns the last value.
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(assert-equal 5 (and t t t t t 5)))
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(define-test or
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;; The logical operator OR can also take multiple arguments.
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(true-or-false? t (or nil nil nil t nil))
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;; OR returns the first non-NIL value it encounters, or NIL if there are none.
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(assert-equal nil (or nil nil nil))
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(assert-equal 1 (or 1 2 3 4 5)))
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