Commit | Line | Data |
---|---|---|
67ad47b7 MW |
1 | \ -*-forth-*- |
2 | \ | |
3 | \ Same-fringe solver in Forth. | |
4 | ||
5 | \ --------------------------------------------------------------------------- | |
6 | \ Utilities. Most of these are GForth-specific in some way. | |
7 | ||
8 | \ String representation conversions. | |
9 | ||
10 | : string>bounds ( c-addr u -- c-addr-limit c-addr ) | |
11 | \ Convert a string in the usual base/length form to a limit/base form | |
12 | \ which is better suited to iteration. The base is left on the top | |
13 | \ because it's likely to change more frequently. | |
14 | chars over + swap ; | |
15 | ||
16 | : bounds>string ( c-addr-limit c-addr -- c-addr u ) | |
17 | \ Convert a string in limit/base form back to base/length form. | |
18 | tuck - [ 1 chars ] literal / ; | |
19 | ||
20 | \ Program name. Want the portion after the rightmost `/'. | |
21 | \ | |
22 | \ Bodge: gforth doesn't want to hand over the image filename so we'll have to | |
23 | \ hardwire. | |
24 | ||
25 | : quis s" forth-fringe" ; | |
26 | ||
27 | \ Error reporting. | |
28 | ||
29 | : ouch ( a-addr u -- program exits ) | |
30 | \ Report an error message on stderr and exit with a nonzero status. | |
31 | quis stderr write-file drop | |
32 | s" : " stderr write-file drop | |
33 | 2dup stderr write-line drop | |
34 | 1 (bye) \ Gforth specific | |
35 | ; | |
36 | ||
37 | \ --------------------------------------------------------------------------- | |
38 | \ Coroutines. Largely very scary. | |
39 | ||
40 | \ A coroutine descriptor consists of a single cell containing the coroutine's | |
41 | \ return-stack pointer. This cell is only valid when the coroutine is | |
42 | \ inactive. | |
43 | \ | |
44 | \ Coroutines have distinct return stacks, but share the main value stack and | |
45 | \ floating-point stack, which they can use for communication with other | |
46 | \ coroutines. A coroutine will therefore typically stash state on the return | |
47 | \ stack. | |
48 | \ | |
49 | \ There's no current provision for Gforth's separate locals stack. | |
50 | ||
51 | \ The amount of return-stack storage we allocate to a coroutine. | |
52 | 256 cells constant cr-space | |
53 | ||
54 | \ The current coroutine. This initially points to an uninitialized | |
55 | \ descriptor which we'll fill in during the first coroutine switch. | |
56 | variable current-cr | |
57 | here current-cr ! cell allot | |
58 | ||
59 | \ The coroutine which invoked this one. This is used by `yield'. | |
60 | variable caller-cr | |
61 | ||
62 | : switch-cr ( cr -- ) | |
63 | \ Make `cr' the current coroutine, and tell it that it was called by this | |
64 | \ one. | |
65 | rp@ current-cr @ ! | |
66 | current-cr @ caller-cr ! | |
67 | dup current-cr ! | |
68 | @ rp! | |
69 | ; | |
70 | ||
71 | : yield ( -- ) | |
72 | \ Make the calling coroutine current again. | |
73 | caller-cr @ switch-cr | |
74 | ; | |
75 | ||
76 | : start-cr ( cr xt -- ) | |
77 | \ Switch to the new coroutine `cr', and have it execute the token `xt'. | |
78 | swap | |
79 | rp@ current-cr @ ! | |
80 | current-cr @ caller-cr ! | |
81 | dup current-cr ! | |
82 | @ rp! | |
83 | execute | |
84 | ; | |
85 | ||
86 | : init-cr ( a-addr -- cr ) | |
87 | \ Initialize a chunk of memory at `a-addr' and turn it into a pointer to | |
88 | \ a coroutine descriptor `cr' ready for use by `start-cr'. | |
89 | [ cr-space cell - ] literal + | |
90 | dup dup ! | |
91 | ; | |
92 | ||
93 | : [alloc-cr] ( -- cr ; R: -- cr-sys ) | |
94 | \ Compile-time word: adjust the return stack pointer, returning a | |
95 | \ coroutine descriptor `cr'. The space can be recovered using | |
96 | \ `[drop-cr]'. This must be done at compile time, because returning is | |
97 | \ hard after you've messed with the return stack pointer. | |
98 | postpone rp@ postpone cr-space postpone - postpone dup | |
99 | postpone rp! postpone init-cr | |
100 | ; immediate | |
101 | ||
102 | : [drop-cr] ( cr -- ; R: cr-sys -- ) | |
103 | \ Compile-time word: adjust the return-stack pointer to reclaim the space | |
104 | \ used for the coroutine `cr' and all those above it on the return stack. | |
105 | postpone cell postpone + postpone rp! | |
106 | ; immediate | |
107 | ||
108 | \ --------------------------------------------------------------------------- | |
109 | \ Iterator protocol. | |
110 | \ | |
111 | \ An iterator is a coroutine which yields a word and a flag. While there are | |
112 | \ items available, it yields items paired with `true' flags; when all items | |
113 | \ are exhausted, it yields a word and a `false' flag. After that, invoking | |
114 | \ the coroutine again is invalid. | |
115 | ||
116 | : print-iterator ( cr -- ) | |
117 | \ Print the characters returned by the iterator coroutine `cr'. | |
118 | begin dup switch-cr while emit repeat | |
119 | drop | |
120 | ; | |
121 | ||
122 | : same-iterators-p ( cr0 cr1 -- f ) | |
123 | \ Report true if the iterator coroutines `cr0' and `cr1' return the same | |
124 | \ items in the same order, as determined by `='. | |
125 | begin | |
126 | over switch-cr ( cr0 cr1 x0 f0 ) | |
127 | 2 pick switch-cr ( cr0 cr1 x0 f0 x1 f1 ) | |
128 | rot ( cr0 cr1 x0 x1 f1 f0 ) | |
129 | over <> if 2drop 2drop drop false exit then | |
130 | 0= if 2drop 2drop true exit then | |
131 | <> if 2drop false exit then | |
132 | again | |
133 | ; | |
134 | ||
135 | \ --------------------------------------------------------------------------- | |
136 | \ Binary trees. | |
137 | ||
138 | : make-tree ( a-addr-left w-datum a-addr-right -- a-addr-tree ) | |
139 | \ Construct a binary tree from components on the stack, returning the | |
140 | \ address of the tree node. | |
141 | here >r \ stash pointer | |
142 | swap rot , , , \ reorder and store | |
143 | r> \ recover pointer | |
144 | ; | |
145 | ||
146 | \ A leaf is an empty tree. The address of this variable is important; its | |
147 | \ contents are not. | |
148 | variable leaf | |
149 | ||
150 | \ Binary tree structure. | |
151 | : tree-left ( a-addr -- a-addr' ) ; | |
152 | : tree-datum ( a-addr -- a-addr' ) cell+ ; | |
153 | : tree-right ( a-addr -- a-addr' ) [ 2 cells ] literal + ; | |
154 | 3 constant tree-ncells | |
155 | ||
156 | : parse-subtree ( c-addr-limit c-addr -- c-addr-limit c-addr' tree ) | |
157 | \ Parse a subtree from the string on the stack (in limit/base form). | |
158 | \ Update the string to reflect how much we consumed, and leave the tree | |
159 | \ address for the caller. See `parse-tree' for the syntax. | |
160 | 2dup > if dup c@ [char] ( <> else true then if | |
161 | leaf | |
162 | else | |
163 | char+ | |
164 | leaf 0 leaf make-tree >r | |
165 | recurse r@ tree-left ! | |
166 | 2dup <= if s" no data" ouch then | |
167 | dup c@ r@ tree-datum ! char+ | |
168 | recurse r@ tree-right ! | |
169 | 2dup <= if true else dup c@ [char] ) <> then if | |
170 | s" missing )" ouch | |
171 | then | |
172 | char+ | |
173 | r> | |
174 | then | |
175 | ; | |
176 | ||
177 | : parse-tree ( c-addr u -- tree ) | |
178 | \ Parse a tree from the string on the stack. | |
179 | \ | |
180 | \ The syntax is simple: | |
181 | \ | |
182 | \ tree :: empty | `(' tree char tree `)' | |
183 | \ | |
184 | \ The ambiguity is resolved by always treating `(' as a tree when a tree | |
185 | \ is expected. | |
186 | string>bounds | |
187 | parse-subtree >r | |
188 | <> if s" trailing junk" ouch then | |
189 | r> | |
190 | ; | |
191 | ||
192 | : do-tree-fringe ( tree -- yields: x f ) | |
193 | \ Helper word for `tree-fringe' below. Recursively yields up the items | |
194 | \ of the subtree rooted at `tree'. | |
195 | dup leaf = if | |
196 | drop | |
197 | else | |
198 | >r | |
199 | r@ tree-left @ recurse | |
200 | r@ tree-datum @ true yield | |
201 | r> tree-right @ recurse | |
202 | then | |
203 | ; | |
204 | ||
205 | : tree-fringe ( tree -- yields: x f ) | |
206 | \ Yield up the items of `tree' in order, according to the iteration | |
207 | \ protocol. | |
208 | >r yield | |
209 | r> do-tree-fringe | |
210 | 0 false yield | |
211 | ; | |
212 | ||
213 | \ --------------------------------------------------------------------------- | |
214 | \ Main program. | |
215 | ||
216 | : main | |
217 | \ Main program: parse arguments and do what's asked for. | |
218 | argc @ case | |
219 | ||
220 | 2 of | |
221 | \ One proper argument: parse a tree and print its fringe. | |
222 | [alloc-cr] | |
223 | 1 arg parse-tree over ['] tree-fringe start-cr | |
224 | dup print-iterator cr | |
225 | [drop-cr] | |
226 | endof | |
227 | ||
228 | 3 of | |
229 | \ Two arguments: parse two trees and compare them. | |
230 | [alloc-cr] 1 arg parse-tree over ['] tree-fringe start-cr | |
231 | dup | |
232 | [alloc-cr] 2 arg parse-tree over ['] tree-fringe start-cr | |
233 | same-iterators-p | |
234 | swap [drop-cr] | |
235 | if ." match" else ." no match" then cr | |
236 | endof | |
237 | ||
238 | \ Default. | |
239 | s" bad args" ouch | |
240 | ||
241 | endcase | |
242 | ; | |
243 | ||
244 | \ Gforth image magic. | |
245 | :noname | |
246 | defers 'cold | |
247 | main | |
248 | bye | |
249 | ; is 'cold | |
250 | ||
251 | \ --------------------------------------------------------------------------- |