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e6591bec MW |
1 | /* -*-c-*- |
2 | * | |
3 | * Control operators, after Simon Tatham | |
4 | * | |
5 | * (c) 2022 Straylight/Edgeware | |
6 | */ | |
7 | ||
8 | /*----- Licensing notice --------------------------------------------------* | |
9 | * | |
10 | * This file is part of the mLib utilities library. | |
11 | * | |
12 | * mLib is free software: you can redistribute it and/or modify it under | |
13 | * the terms of the GNU Library General Public License as published by | |
14 | * the Free Software Foundation; either version 2 of the License, or (at | |
15 | * your option) any later version. | |
16 | * | |
17 | * mLib is distributed in the hope that it will be useful, but WITHOUT | |
18 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
19 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public | |
20 | * License for more details. | |
21 | * | |
22 | * You should have received a copy of the GNU Library General Public | |
23 | * License along with mLib. If not, write to the Free Software | |
24 | * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, | |
25 | * USA. | |
26 | */ | |
27 | ||
28 | #ifndef MLIB_CONTROL_H | |
29 | #define MLIB_CONTROL_H | |
30 | ||
31 | #ifdef __cplusplus | |
32 | extern "C" { | |
33 | #endif | |
34 | ||
35 | /*----- Header files ------------------------------------------------------*/ | |
36 | ||
37 | #ifndef MLIB_MACROS_H | |
38 | # include "macros.h" | |
39 | #endif | |
40 | ||
41 | /*----- Macros provided ---------------------------------------------------*/ | |
42 | ||
43 | /* @MCTRL__LABEL(tag)@ * | |
44 | * | |
45 | * Expand to a plausibly unique label based on the current line number and | |
46 | * the @tag@. | |
47 | */ | |
48 | #define MCTRL__LABEL(tag) GLUE(_mctrl__##tag##__, __LINE__) | |
49 | ||
2edecb46 MW |
50 | /* @MC_ACT(stmt)@ |
51 | * @MC_PASS@ | |
52 | * | |
53 | * @MC_ACT@ is the main `trick' for constructing these flow-control | |
54 | * operators. It wraps up a statement as what we call an `action'. Actions | |
55 | * can be concatenated together to form a valid statement head, i.e., a | |
56 | * sequence of actions can be followed by a statement, called the `body', to | |
57 | * form a single syntactic statement. The body can be simply `;', so an | |
58 | * action can be treated as a simple statement. However, if an action | |
59 | * sequence is executed, only the first statement is executed. | |
60 | * | |
61 | * Actions can be labelled, e.g., using @MC_LABEL@, just like statements. If | |
62 | * control is passed to a label, e.g., by @MC_GOTO@, then the statement | |
63 | * within the following action (only) is executed; the normal flow of control | |
64 | * will then be to the statement following the containing action sequence and | |
65 | * its body. | |
66 | */ | |
491f4344 | 67 | #define MC_ACT(stmt) if (1) { stmt; } else |
2edecb46 MW |
68 | #define MC_PASS MC_ACT(;) |
69 | ||
70 | ||
71 | /* @MC_LABEL(tag)@ | |
72 | * @MC_GOTO(tag)@ | |
73 | * | |
74 | * @MC_LABEL@ just establishes a label which can be invoked (only) from the | |
75 | * same top-level macro; and @MC_GOTO@ transfers control to it. | |
76 | * | |
77 | * The @MC_GOTO@ macro is special in that it can be used either as a plain | |
78 | * statement, followed by a semicolon in the usual way, or as a prefix | |
79 | * action in its own right, in place of @MC_ACT@. | |
e6591bec | 80 | */ |
2edecb46 | 81 | #define MC_LABEL(tag) MCTRL__LABEL(tag): |
491f4344 | 82 | #define MC_GOTO(tag) MC_ACT(goto MCTRL__LABEL(tag)) |
e6591bec MW |
83 | |
84 | /* @BEFORE(tag, stmt_0) stmt_1@ | |
85 | * | |
86 | * Execute @stmt_0@ and then @stmt_1@. | |
87 | */ | |
88 | #define BEFORE(tag, stmt) \ | |
491f4344 | 89 | MC_ACT(stmt; MC_GOTO(tag##__body)) \ |
2edecb46 | 90 | MC_LABEL(tag##__body) |
e6591bec MW |
91 | |
92 | /* @AFTER(tag, stmt_0) stmt_1@ | |
93 | * | |
94 | * Execute @stmt_1@ and then @stmt_0@. If either statement invokes @break@ | |
95 | * then control immediately transfers to the statement following @AFTER@. If | |
96 | * either invokes @continue@, then control returns to @stmt_0@. | |
97 | */ | |
98 | #define AFTER(tag, stmt) \ | |
2edecb46 MW |
99 | MC_GOTO(tag##__body) \ |
100 | MC_LABEL(tag##__end) MC_ACT(stmt) \ | |
101 | for (;;) \ | |
102 | MC_GOTO(tag##__end) \ | |
103 | MC_LABEL(tag##__body) | |
e6591bec MW |
104 | |
105 | /* @WRAP(tag, before, onend, onbreak) stmt@ | |
106 | * | |
107 | * Execute the @before@ statement, followed by @stmt@. If @stmt@ invokes | |
108 | * @break@, then @onbreak@ is immediately executed; if @stmt@ completes | |
109 | * normally, or invokes @continue@ then @onend@ is immediately executed. | |
110 | * Any @break@ and @continue@ in the @before@, @onend@, and @onbreak@ | |
111 | * statements behave as one would expect from their context. | |
112 | */ | |
113 | #define WRAP(tag, before, onend, onbreak) \ | |
491f4344 | 114 | MC_ACT(before; MC_GOTO(tag##__body)) \ |
2edecb46 MW |
115 | MC_LABEL(tag##__end) MC_ACT(onend) \ |
116 | MC_LABEL(tag##__brk) MC_ACT(onbreak) \ | |
117 | for (;;) \ | |
118 | MC_GOTO(tag##__brk) \ | |
119 | for (;;) \ | |
120 | MC_GOTO(tag##__end) \ | |
121 | MC_LABEL(tag##__body) | |
122 | ||
123 | /* @ALLOWELSE(tag) stmt_0 [else stmt_1]@ | |
e6591bec MW |
124 | * @GOELSE(tag);@ |
125 | * | |
2edecb46 MW |
126 | * Executing @ALLOWELSE@ executes @stmt_0@, but not @stmt_1@. If |
127 | * @GOELSE(tag)@ is executed, then control continues from @stmt_1@. | |
e6591bec | 128 | */ |
2edecb46 MW |
129 | #define ALLOWELSE(tag) \ |
130 | MC_GOTO(tag##__body) \ | |
131 | MC_LABEL(tag##__else) if (0) \ | |
132 | MC_LABEL(tag##__body) | |
133 | #define GOELSE(tag) do MC_GOTO(tag##__else); while (0) | |
e6591bec MW |
134 | |
135 | /* @DOWHILE(tag, cond) stmt@ | |
136 | * | |
137 | * Repeatedly execute @stmt@ until @cond@ evaluates to zero. Execute @stmt@ | |
138 | * at least once. The @break@ and @continue@ statements work within @stmt@ | |
139 | * as one would expect. | |
140 | */ | |
141 | #define DOWHILE(tag, cond) \ | |
2edecb46 MW |
142 | MC_GOTO(tag##__body) \ |
143 | while (cond) \ | |
144 | MC_LABEL(tag##__body) | |
e6591bec MW |
145 | |
146 | /* @DECL(tag, decl) stmt@ | |
147 | * | |
148 | * Execute @stmt@ with @decl@ in scope. If @stmt@ completes or invokes | |
149 | * @break@ or @continue@ then control continues with the statement following | |
150 | * @DECL@. Internally, this uses @for@, so it only works in C99 or later, or | |
151 | * C++. | |
152 | */ | |
153 | #if __STDC_VERSION__ >= 199901 || defined(__cplusplus) | |
154 | # define DECL(tag, decl) \ | |
2edecb46 MW |
155 | for (decl;;) \ |
156 | MC_GOTO(tag##__body) \ | |
491f4344 | 157 | MC_LABEL(tag##__end) MC_ACT(break) \ |
2edecb46 MW |
158 | for (;;) \ |
159 | MC_GOTO(tag##__end) \ | |
160 | MC_LABEL(tag##__body) | |
e6591bec MW |
161 | #endif |
162 | ||
163 | /*----- That's all, folks -------------------------------------------------*/ | |
164 | ||
165 | #ifdef __cplusplus | |
166 | } | |
167 | #endif | |
168 | ||
169 | #endif |