63 lines
2.1 KiB
Common Lisp
63 lines
2.1 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 let
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;; The LET form establishes a lexical extent within which new variables are
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;; created: a symbol that names a variable becomes bound to a value.
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(let ((x 10)
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(y 20))
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(assert-equal 30 (+ x y))
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;; It is possible to shadow previously visible bindings.
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(let ((y 30))
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(assert-equal 40 (+ x y)))
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(assert-equal 30 (+ x y)))
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;; Variables bound by LET have a default value of NIL.
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(let (x)
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(assert-equal nil x)))
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(define-test let-versus-let*
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;; LET* is similar to LET, except the bindings are established sequentially,
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;; and a binding may use bindings that were established before it.
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(let ((x 10)
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(y 20))
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(let ((x (+ y 100))
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(y (+ x 100)))
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(assert-equal 120 x)
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(assert-equal 110 y))
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(let* ((x (+ y 100))
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(y (+ x 100)))
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;; Which X is used to compute the value of Y?
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(assert-equal 120 x)
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(assert-equal 220 y))))
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(define-test let-it-be-equal
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;; Fill in the LET and LET* to get the tests to pass.
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(let ((a 1)
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(b :two)
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(c "Three"))
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(let ((a 100)
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(b 200)
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(c "Jellyfish"))
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(assert-equal a 100)
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(assert-equal b 200)
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(assert-equal c "Jellyfish"))
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(let* ((a 121)
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(b 200)
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;; In this third binding, you are allowed to use the variables bound
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;; by the previous two LET* bindings.
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(c (+ a (/ b a))))
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(assert-equal a 121)
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(assert-equal b 200)
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(assert-equal c (+ a (/ b a))))))
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