63 lines
2.1 KiB
Common Lisp
63 lines
2.1 KiB
Common Lisp
;;; Copyright 2013 Google Inc.
|
|
;;;
|
|
;;; Licensed under the Apache License, Version 2.0 (the "License");
|
|
;;; you may not use this file except in compliance with the License.
|
|
;;; You may obtain a copy of the License at
|
|
;;;
|
|
;;; http://www.apache.org/licenses/LICENSE-2.0
|
|
;;;
|
|
;;; Unless required by applicable law or agreed to in writing, software
|
|
;;; distributed under the License is distributed on an "AS IS" BASIS,
|
|
;;; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
|
;;; See the License for the specific language governing permissions and
|
|
;;; limitations under the License.
|
|
|
|
(define-test let
|
|
;; The LET form establishes a lexical extent within which new variables are
|
|
;; created: a symbol that names a variable becomes bound to a value.
|
|
(let ((x 10)
|
|
(y 20))
|
|
(assert-equal 30 (+ x y))
|
|
;; It is possible to shadow previously visible bindings.
|
|
(let ((y 30))
|
|
(assert-equal 40 (+ x y)))
|
|
(assert-equal 30 (+ x y)))
|
|
;; Variables bound by LET have a default value of NIL.
|
|
(let (x)
|
|
(assert-equal nil x)))
|
|
|
|
(define-test let-versus-let*
|
|
;; LET* is similar to LET, except the bindings are established sequentially,
|
|
;; and a binding may use bindings that were established before it.
|
|
(let ((x 10)
|
|
(y 20))
|
|
(let ((x (+ y 100))
|
|
(y (+ x 100)))
|
|
(assert-equal 120 x)
|
|
(assert-equal 110 y))
|
|
(let* ((x (+ y 100))
|
|
(y (+ x 100)))
|
|
;; Which X is used to compute the value of Y?
|
|
(assert-equal 120 x)
|
|
(assert-equal 220 y))))
|
|
|
|
(define-test let-it-be-equal
|
|
;; Fill in the LET and LET* to get the tests to pass.
|
|
(let ((a 1)
|
|
(b :two)
|
|
(c "Three"))
|
|
(let ((a 100)
|
|
(b (* 200 a))
|
|
(c "Jellyfish"))
|
|
(assert-equal a 100)
|
|
(assert-equal b 200)
|
|
(assert-equal c "Jellyfish"))
|
|
(let* ((a 121)
|
|
(b (+ a 79))
|
|
;; In this third binding, you are allowed to use the variables bound
|
|
;; by the previous two LET* bindings.
|
|
(c (+ a (/ b a))))
|
|
(assert-equal a 121)
|
|
(assert-equal b 200)
|
|
(assert-equal c (+ a (/ b a))))))
|