1042
|
1 |
"
|
|
2 |
COPYRIGHT (c) 2002 by eXept Software AG
|
|
3 |
All Rights Reserved
|
|
4 |
|
|
5 |
This software is furnished under a license and may be used
|
|
6 |
only in accordance with the terms of that license and with the
|
|
7 |
inclusion of the above copyright notice. This software may not
|
|
8 |
be provided or otherwise made available to, or used by, any
|
|
9 |
other person. No title to or ownership of the software is
|
|
10 |
hereby transferred.
|
|
11 |
"
|
|
12 |
|
|
13 |
"{ Package: 'stx:libbasic2' }"
|
|
14 |
|
|
15 |
nil subclass:#LazyValue
|
|
16 |
instanceVariableNames:'result block'
|
|
17 |
classVariableNames:'AccessLock'
|
|
18 |
poolDictionaries:''
|
|
19 |
category:'Kernel-Processes'
|
|
20 |
!
|
|
21 |
|
|
22 |
!LazyValue class methodsFor:'documentation'!
|
|
23 |
|
|
24 |
copyright
|
|
25 |
"
|
|
26 |
COPYRIGHT (c) 2002 by eXept Software AG
|
|
27 |
All Rights Reserved
|
|
28 |
|
|
29 |
This software is furnished under a license and may be used
|
|
30 |
only in accordance with the terms of that license and with the
|
|
31 |
inclusion of the above copyright notice. This software may not
|
|
32 |
be provided or otherwise made available to, or used by, any
|
|
33 |
other person. No title to or ownership of the software is
|
|
34 |
hereby transferred.
|
|
35 |
"
|
|
36 |
!
|
|
37 |
|
|
38 |
documentation
|
|
39 |
"
|
|
40 |
I represent an expression which might not be needed.
|
|
41 |
Any messages sent to me will force the evaluation (once).
|
|
42 |
The value is remembered.
|
|
43 |
|
|
44 |
Can be used to simulate non-strict programming languages.
|
|
45 |
|
|
46 |
[see also:]
|
|
47 |
Block Future
|
|
48 |
|
|
49 |
[author:]
|
|
50 |
Claus Gittinger
|
|
51 |
"
|
|
52 |
!
|
|
53 |
|
|
54 |
examples
|
|
55 |
"
|
1071
|
56 |
[exBegin]
|
|
57 |
|x|
|
|
58 |
|
|
59 |
x := LazyValue block:[ Transcript flash. 1234 ].
|
|
60 |
Delay waitForSeconds:4.
|
|
61 |
Transcript showCR:x printString
|
|
62 |
[exEnd]
|
|
63 |
|
1042
|
64 |
listFrom:n - an infinite list of integers starting with n
|
|
65 |
[exBegin]
|
|
66 |
|gen infiniteList|
|
|
67 |
|
|
68 |
gen := [:n |
|
|
69 |
Cons
|
|
70 |
car:n
|
|
71 |
cdr:( LazyValue block:[gen value:n+1] )
|
|
72 |
].
|
|
73 |
|
|
74 |
infiniteList := gen value:1.
|
|
75 |
1 to:10 do:[:i |
|
|
76 |
Transcript showCR:infiniteList car.
|
|
77 |
infiniteList := infiniteList cdr.
|
|
78 |
].
|
|
79 |
[exEnd]
|
|
80 |
|
|
81 |
filterOdd:l - an infinite list filtering odd numbers from another list
|
|
82 |
[exBegin]
|
|
83 |
|gen infiniteList genOdd infiniteOdd|
|
|
84 |
|
|
85 |
gen := [:n |
|
|
86 |
Cons
|
|
87 |
car:n
|
|
88 |
cdr:( LazyValue block:[gen value:n+1] )
|
|
89 |
].
|
|
90 |
|
|
91 |
infiniteList := gen value:1.
|
|
92 |
|
|
93 |
genOdd := [:l |
|
|
94 |
|lR el|
|
|
95 |
|
|
96 |
lR := l.
|
|
97 |
[ el := lR car. lR := lR cdr. el odd ] whileFalse:[].
|
|
98 |
Cons
|
|
99 |
car:el
|
|
100 |
cdr:( LazyValue block:[genOdd value:lR] )
|
|
101 |
].
|
|
102 |
|
|
103 |
infiniteOdd := genOdd value:infiniteList.
|
|
104 |
|
|
105 |
1 to:10 do:[:i |
|
|
106 |
Transcript showCR:infiniteOdd car.
|
|
107 |
infiniteOdd := infiniteOdd cdr.
|
|
108 |
].
|
|
109 |
[exEnd]
|
|
110 |
|
|
111 |
powersOf:n - an infinite list of powers of n
|
|
112 |
[exBegin]
|
|
113 |
|genPowersOf infiniteListOfPowers|
|
|
114 |
|
|
115 |
genPowersOf := [:base |
|
|
116 |
|powersOfBase|
|
|
117 |
|
|
118 |
powersOfBase :=
|
|
119 |
[:n |
|
|
120 |
Cons
|
|
121 |
car:n
|
|
122 |
cdr:( LazyValue block:[powersOfBase value:n*base] )
|
|
123 |
].
|
|
124 |
powersOfBase value:1.
|
|
125 |
].
|
|
126 |
|
|
127 |
infiniteListOfPowers := genPowersOf value:2.
|
|
128 |
1 to:10 do:[:i |
|
|
129 |
Transcript showCR:infiniteListOfPowers car.
|
|
130 |
infiniteListOfPowers := infiniteListOfPowers cdr.
|
|
131 |
].
|
|
132 |
[exEnd]
|
|
133 |
|
|
134 |
merge2:a _:b - merge 2 lists.
|
|
135 |
[exBegin]
|
|
136 |
|genMerge2 l gen infiniteList genOdd infiniteOdd genEven infiniteEven genMerge|
|
|
137 |
|
|
138 |
gen := [:n |
|
|
139 |
Cons
|
|
140 |
car:n
|
|
141 |
cdr:( LazyValue block:[gen value:n+1] )
|
|
142 |
].
|
|
143 |
|
|
144 |
infiniteList := gen value:1.
|
|
145 |
|
|
146 |
genOdd := [:l |
|
|
147 |
|lR el|
|
|
148 |
|
|
149 |
lR := l.
|
|
150 |
[ el := lR car. lR := lR cdr. el odd ] whileFalse:[].
|
|
151 |
Cons
|
|
152 |
car:el
|
|
153 |
cdr:( LazyValue block:[genOdd value:lR] )
|
|
154 |
].
|
|
155 |
|
|
156 |
infiniteOdd := genOdd value:infiniteList.
|
|
157 |
|
|
158 |
genEven := [:l |
|
|
159 |
|lR el|
|
|
160 |
|
|
161 |
lR := l.
|
|
162 |
[ el := lR car. lR := lR cdr. el even ] whileFalse:[].
|
|
163 |
Cons
|
|
164 |
car:el
|
|
165 |
cdr:( LazyValue block:[genEven value:lR] )
|
|
166 |
].
|
|
167 |
|
|
168 |
infiniteEven := genEven value:infiniteList.
|
|
169 |
|
|
170 |
genMerge2 := [:a :b |
|
|
171 |
|nextA nextB|
|
|
172 |
|
|
173 |
nextA := a car.
|
|
174 |
nextB := b car.
|
|
175 |
|
|
176 |
nextA < nextB ifTrue:[
|
|
177 |
Cons
|
|
178 |
car:nextA
|
|
179 |
cdr:( LazyValue block:[genMerge2 value:(a cdr) value:b] )
|
|
180 |
] ifFalse:[
|
|
181 |
Cons
|
|
182 |
car:nextB
|
|
183 |
cdr:( LazyValue block:[genMerge2 value:a value:(b cdr)] )
|
|
184 |
].
|
|
185 |
].
|
|
186 |
|
|
187 |
l := genMerge2 value:infiniteOdd value:infiniteEven.
|
|
188 |
1 to:10 do:[:i |
|
|
189 |
Transcript showCR:l car.
|
|
190 |
l := l cdr.
|
|
191 |
].
|
|
192 |
[exEnd]
|
|
193 |
|
|
194 |
genPoly - generate 2^i + 3^j + 5^k for all i,j,k
|
|
195 |
not finished.
|
|
196 |
[exBegin]
|
|
197 |
|genMerge2 l gen genPowersOf infiniteList powersOf2 powersOf3 powersOf5|
|
|
198 |
|
|
199 |
gen := [:n |
|
|
200 |
Cons
|
|
201 |
car:n
|
|
202 |
cdr:( LazyValue block:[gen value:n+1] )
|
|
203 |
].
|
|
204 |
|
|
205 |
infiniteList := gen value:1.
|
|
206 |
|
|
207 |
genPowersOf := [:base |
|
|
208 |
|powersOfBase|
|
|
209 |
|
|
210 |
powersOfBase :=
|
|
211 |
[:n |
|
|
212 |
Cons
|
|
213 |
car:n
|
|
214 |
cdr:( LazyValue block:[powersOfBase value:n*base] )
|
|
215 |
].
|
|
216 |
powersOfBase value:1.
|
|
217 |
].
|
|
218 |
|
|
219 |
powersOf2 := genPowersOf value:2.
|
|
220 |
powersOf3 := genPowersOf value:3.
|
|
221 |
powersOf5 := genPowersOf value:5.
|
|
222 |
|
|
223 |
genAdd := [:n :l |
|
|
224 |
|gen|
|
|
225 |
|
|
226 |
gen := [:l |
|
|
227 |
Cons
|
|
228 |
car:(car l) * n
|
|
229 |
cdr:( LazyValue block:[gen value:(l cdr)] )
|
|
230 |
].
|
|
231 |
gen value:l
|
|
232 |
].
|
|
233 |
|
|
234 |
genMerge2 := [:a :b |
|
|
235 |
|min nextA nextB rA rB|
|
|
236 |
|
|
237 |
rA := a.
|
|
238 |
rB := b.
|
|
239 |
nextA := rA car.
|
|
240 |
[ (nextB := rB car) = nextA ] whileTrue:[ rB := rB cdr ].
|
|
241 |
|
|
242 |
nextA < nextB ifTrue:[
|
|
243 |
'a is smallest'.
|
|
244 |
min := nextA.
|
|
245 |
rA := rA cdr.
|
|
246 |
] ifFalse:[
|
|
247 |
'b is smallest'.
|
|
248 |
min := nextB.
|
|
249 |
rB := rB cdr.
|
|
250 |
].
|
|
251 |
|
|
252 |
Cons
|
|
253 |
car:min
|
|
254 |
cdr:( LazyValue block:[genMerge2 value:rA value:rB] )
|
|
255 |
].
|
|
256 |
|
|
257 |
l := genMerge2 value:powersOf2 value:powersOf3 value:powersOf5.
|
|
258 |
1 to:10 do:[:i |
|
|
259 |
Transcript showCR:l car.
|
|
260 |
l := l cdr.
|
|
261 |
].
|
|
262 |
[exEnd]
|
|
263 |
|
|
264 |
"
|
|
265 |
! !
|
|
266 |
|
|
267 |
!LazyValue class methodsFor:'initialization'!
|
|
268 |
|
|
269 |
initialize
|
|
270 |
AccessLock := RecursionLock forMutualExclusion
|
|
271 |
! !
|
|
272 |
|
|
273 |
!LazyValue class methodsFor:'instance creation'!
|
|
274 |
|
|
275 |
block:aBlock
|
|
276 |
^ self new block:aBlock
|
|
277 |
! !
|
|
278 |
|
|
279 |
!LazyValue methodsFor:'error handling'!
|
|
280 |
|
|
281 |
doesNotUnderstand:aMessage
|
|
282 |
block notNil ifTrue:[
|
|
283 |
self _evaluate_
|
|
284 |
].
|
|
285 |
^ aMessage sendTo:result
|
|
286 |
! !
|
|
287 |
|
|
288 |
!LazyValue methodsFor:'evaluation'!
|
|
289 |
|
|
290 |
_evaluate_
|
|
291 |
block notNil ifTrue:[
|
|
292 |
AccessLock critical:[
|
|
293 |
|b|
|
|
294 |
|
1071
|
295 |
(b := block) notNil ifTrue:[
|
1042
|
296 |
block := nil.
|
|
297 |
result := b value.
|
|
298 |
].
|
|
299 |
].
|
|
300 |
].
|
|
301 |
^ result
|
|
302 |
! !
|
|
303 |
|
|
304 |
!LazyValue methodsFor:'printing'!
|
|
305 |
|
1071
|
306 |
displayString
|
|
307 |
block isNil ifTrue:[
|
|
308 |
^ 'LazyValue (unevaluated)'
|
|
309 |
].
|
|
310 |
^ 'LazyValue (evaluated)'
|
|
311 |
!
|
|
312 |
|
1042
|
313 |
printOn:aStream
|
|
314 |
aStream nextPutAll:'(lazy)'
|
|
315 |
! !
|
|
316 |
|
|
317 |
!LazyValue methodsFor:'private access'!
|
|
318 |
|
|
319 |
block:aBlock
|
|
320 |
block := aBlock.
|
|
321 |
! !
|
|
322 |
|
|
323 |
!LazyValue methodsFor:'queries'!
|
|
324 |
|
|
325 |
class
|
|
326 |
^ self _evaluate_ class
|
|
327 |
!
|
|
328 |
|
|
329 |
isLazyValue
|
|
330 |
^ block notNil
|
|
331 |
! !
|
|
332 |
|
|
333 |
!LazyValue methodsFor:'testing'!
|
|
334 |
|
|
335 |
isBehavior
|
|
336 |
^ self _evaluate_ isBehavior
|
|
337 |
! !
|
|
338 |
|
|
339 |
!LazyValue class methodsFor:'documentation'!
|
|
340 |
|
|
341 |
version
|
1071
|
342 |
^ '$Header: /cvs/stx/stx/libbasic2/LazyValue.st,v 1.2 2002-07-25 14:38:51 cg Exp $'
|
1042
|
343 |
! !
|
|
344 |
LazyValue initialize!
|