source: project/release/5/list-comprehensions/tags/1.0/list-comprehensions.scm @ 37163

Last change on this file since 37163 was 37163, checked in by juergen, 10 months ago

list-comprehensions 1.0 initial import

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1; Author: Juergen Lorenz ; ju (at) jugilo (dot) de
2;
3; Copyright (c) 2017-2019, Juergen Lorenz
4; All rights reserved.
5;
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7; modification, are permitted provided that the following conditions are
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9;
10; Redistributions of source code must retain the above copyright
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13; Redistributions in binary form must reproduce the above copyright
14; notice, this list of conditions and the following dispasser in the
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20;
21; THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
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23; TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
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30; NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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32
33
34#|[
35This module implements some list creating routines, in particular a
36version of Clojure's equally named macro for, which is to replace
37list-comprehension syntax, e.g. [n^2 | n<-[1..10]; n mod 2 = 0]
38of purely functional languages like Miranda.
39]|#
40
41(module list-comprehensions
42  (list-comprehensions for range repeat
43   iterate-while iterate-until iterate-times)
44
45  (import scheme
46          (only (chicken base) case-lambda error print))
47
48(define range
49  (case-lambda
50    ((upto)
51     (if (>= upto 0)
52       (range 0 upto 1)
53       (range 0 upto -1)))
54    ((from upto)
55     (if (>= upto from)
56       (range from upto 1)
57       (range from upto -1)))
58    ((from upto step)
59     (cond
60       ((and (>= upto from) (positive? step))
61        (let loop ((k from) (result '()))
62          (if (>= k upto)
63            (reverse result)
64            (loop (+ k step) (cons k result)))))
65       ((and (< upto from) (negative? step))
66        (let loop ((k from) (result '()))
67          (if (<= k upto)
68            (reverse result)
69            (loop (+ k step) (cons k result)))))
70       (else
71         (error 'range "wrong sign of" step))))))
72
73(define (repeat times)
74  (lambda (x)
75    (let loop ((k 0) (result '()))
76      (if (= k times)
77        result
78        (loop (+ k 1) (cons x result))))))
79
80(define (iterate-while fn ok?)
81  (lambda (start)
82    (let loop ((var start) (result '()))
83      (if (ok? var)
84        (loop (fn var) (cons var result))
85        (reverse result)))))
86
87(define (iterate-until fn ok?)
88  (lambda (start)
89    (let loop ((var start) (result '()))
90      (if (ok? var)
91        (reverse result)
92        (loop (fn var) (cons var result))))))
93
94(define (iterate-times fn times)
95  (lambda (start)
96    (let loop ((var start) (k 0) (result '()))
97      (if (= k times)
98        (reverse result)
99        (loop (fn var) (+ k 1) (cons var result))))))
100
101;;; (for ((var lst fltr ...) ....) item)
102;;; ------------------------------------
103(define-syntax for
104  (syntax-rules ()
105   ((_ ((var lst fltr ...)) item)
106     (let recur ((seq lst))
107       (if (null? seq)
108         '()
109         (let ((var (car seq)))
110           (if (and fltr ...)
111             (cons item (recur (cdr seq)))
112             (recur (cdr seq)))))))
113    ((_ ((var lst fltr ...) (var1 lst1 fltr1 ...) ...) item)
114     (let recur ((seq lst))
115       (if (null? seq)
116         '()
117         (let ((var (car seq)))
118           (if (and fltr ...)
119             (append (for ((var1 lst1 fltr1 ...) ...) item)
120                     (recur (cdr seq)))
121             (recur (cdr seq)))))))
122    ))
123
124   
125;;; (list-comprehensions sym ..)
126;;; ----------------------------
127;;; documentation procedure
128(define list-comprehensions
129  (let ((als '(
130    (list-comprehensions
131      procedure:
132      (list-comprehensions sym ..)
133      "documentation procedure")
134    (range
135      procedure:
136      (range upto)
137      (range from upto)
138      (range from upto step)
139      "creates a list of numbers with given limits"
140      "from defaults to 0"
141      "step defaults to 1")
142    (repeat
143      procedure:
144      (repeat times)
145      "returns a unary procedure which repeats its only argument"
146      "a number of times")
147    (iterate-times
148      procedure:
149      (iterate-times fn times)
150      "returns a unary procedure which iterates the function fn"
151      "on its only argument a number of times")
152    (iterate-while
153      procedure:
154      (iterate-while fn ok?)
155      "returns a unary procedure which iterates the function fn"
156      "on its only argument while the predicate ok? returns true")
157    (iterate-until
158      procedure:
159      (iterate-until fn ok?)
160      "returns a unary procedure which iterates the function fn"
161      "on its only argument until the predicate ok? returns true")
162    (for
163      macro:
164      (for ((var lst fltr ...) ....) item)
165      "creates a new list by binding var to each element"
166      "of the list lst in sequence, and if it passes the checks,"
167      "fltr ..., inserts item into the result list."
168      "The qualifieres, (var lst fltr ...), are processed"
169      "sequentially from left to right, so that filters of a"
170      "qualifier have access to the variables of qualifiers"
171      "to its left.")
172    )))
173    (case-lambda
174      (()
175       (map car als))
176      ((sym)
177       (let ((pair (assq sym als)))
178         (if pair
179           (for-each print (cdr pair))
180           (error "Not in list"
181                  sym
182                  (map car als))))))))
183
184) ; module list-comprehensions
185
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