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1 | %%% -*-latex-*- |
2 | %%% | |
3 | %%% Module syntax | |
4 | %%% | |
5 | %%% (c) 2015 Straylight/Edgeware | |
6 | %%% | |
7 | ||
8 | %%%----- Licensing notice --------------------------------------------------- | |
9 | %%% | |
10 | %%% This file is part of the Sensble Object Design, an object system for C. | |
11 | %%% | |
12 | %%% SOD is free software; you can redistribute it and/or modify | |
13 | %%% it under the terms of the GNU General Public License as published by | |
14 | %%% the Free Software Foundation; either version 2 of the License, or | |
15 | %%% (at your option) any later version. | |
16 | %%% | |
17 | %%% SOD is distributed in the hope that it will be useful, | |
18 | %%% but WITHOUT ANY WARRANTY; without even the implied warranty of | |
19 | %%% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
20 | %%% GNU General Public License for more details. | |
21 | %%% | |
22 | %%% You should have received a copy of the GNU General Public License | |
23 | %%% along with SOD; if not, write to the Free Software Foundation, | |
24 | %%% Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. | |
25 | ||
26 | \chapter{Module syntax} \label{ch:syntax} | |
27 | ||
28 | %%%-------------------------------------------------------------------------- | |
29 | ||
30 | Fortunately, Sod is syntactically quite simple. I've used a little slightly | |
31 | unusual notation in order to make the presentation easier to read. For any | |
32 | nonterminal $x$: | |
33 | \begin{itemize} | |
34 | \item $\epsilon$ denotes the empty nonterminal: | |
35 | \begin{quote} | |
36 | $\epsilon$ ::= | |
37 | \end{quote} | |
38 | \item @[$x$@] means an optional $x$: | |
39 | \begin{quote} | |
40 | \syntax{@[$x$@] ::= $\epsilon$ @! $x$} | |
41 | \end{quote} | |
42 | \item $x^*$ means a sequence of zero or more $x$s: | |
43 | \begin{quote} | |
44 | \syntax{$x^*$ ::= $\epsilon$ @! $x^*$ $x$} | |
45 | \end{quote} | |
46 | \item $x^+$ means a sequence of one or more $x$s: | |
47 | \begin{quote} | |
48 | \syntax{$x^+$ ::= $x$ $x^*$} | |
49 | \end{quote} | |
50 | \item $x$@<-list> means a sequence of one or more $x$s separated | |
51 | by commas: | |
52 | \begin{quote} | |
53 | \syntax{$x$<-list> ::= $x$ @! $x$<-list> "," $x$} | |
54 | \end{quote} | |
55 | \end{itemize} | |
56 | ||
57 | \subsection{Lexical syntax} | |
58 | \label{sec:syntax.lex} | |
59 | ||
60 | Whitespace and comments are discarded. The remaining characters are | |
61 | collected into tokens according to the following syntax. | |
62 | ||
63 | \begin{grammar} | |
64 | <token> ::= <identifier> | |
65 | \alt <string-literal> | |
66 | \alt <char-literal> | |
67 | \alt <integer-literal> | |
68 | \alt <punctuation> | |
69 | \end{grammar} | |
70 | ||
71 | This syntax is slightly ambiguous, and is disambiguated by the \emph{maximal | |
72 | munch} rule: at each stage we take the longest sequence of characters which | |
73 | could be a token. | |
74 | ||
75 | \subsubsection{Identifiers} \label{sec:syntax.lex.id} | |
76 | ||
77 | \begin{grammar} | |
78 | <identifier> ::= <id-start-char> @<id-body-char>^* | |
79 | ||
80 | <id-start-char> ::= <alpha-char> | "_" | |
81 | ||
82 | <id-body-char> ::= <id-start-char> @! <digit-char> | |
83 | ||
84 | <alpha-char> ::= "A" | "B" | \dots\ | "Z" | |
85 | \alt "a" | "b" | \dots\ | "z" | |
86 | \alt <extended-alpha-char> | |
87 | ||
88 | <digit-char> ::= "0" | <nonzero-digit-char> | |
89 | ||
90 | <nonzero-digit-char> ::= "1" | "2" $| \cdots |$ "9" | |
91 | \end{grammar} | |
92 | ||
93 | The precise definition of @<alpha-char> is left to the function | |
94 | \textsf{alpha-char-p} in the hosting Lisp system. For portability, | |
95 | programmers are encouraged to limit themselves to the standard ASCII letters. | |
96 | ||
97 | There are no reserved words at the lexical level, but the higher-level syntax | |
98 | recognizes certain identifiers as \emph{keywords} in some contexts. There is | |
99 | also an ambiguity (inherited from C) in the declaration syntax which is | |
100 | settled by distinguishing type names from other identifiers at a lexical | |
101 | level. | |
102 | ||
103 | \subsubsection{String and character literals} \label{sec:syntax.lex.string} | |
104 | ||
105 | \begin{grammar} | |
106 | <string-literal> ::= "\"" @<string-literal-char>^* "\"" | |
107 | ||
108 | <char-literal> ::= "'" <char-literal-char> "'" | |
109 | ||
110 | <string-literal-char> ::= any character other than "\\" or "\"" | |
111 | \alt "\\" <char> | |
112 | ||
113 | <char-literal-char> ::= any character other than "\\" or "'" | |
114 | \alt "\\" <char> | |
115 | ||
116 | <char> ::= any single character | |
117 | \end{grammar} | |
118 | ||
119 | The syntax for string and character literals differs from~C. In particular, | |
120 | escape sequences such as @`\textbackslash n' are not recognized. The use | |
121 | of string and character literals in Sod, outside of C~fragments, is limited, | |
122 | and the simple syntax seems adequate. For the sake of future compatibility, | |
123 | the use of character sequences which resemble C escape sequences is | |
124 | discouraged. | |
125 | ||
126 | \subsubsection{Integer literals} \label{sec:syntax.lex.int} | |
127 | ||
128 | \begin{grammar} | |
129 | <integer-literal> ::= <decimal-integer> | |
130 | \alt <binary-integer> | |
131 | \alt <octal-integer> | |
132 | \alt <hex-integer> | |
133 | ||
134 | <decimal-integer> ::= <nonzero-digit-char> @<digit-char>^* | |
135 | ||
136 | <binary-integer> ::= "0" @("b"|"B"@) @<binary-digit-char>^+ | |
137 | ||
138 | <binary-digit-char> ::= "0" | "1" | |
139 | ||
140 | <octal-integer> ::= "0" @["o"|"O"@] @<octal-digit-char>^+ | |
141 | ||
142 | <octal-digit-char> ::= "0" | "1" $| \cdots |$ "7" | |
143 | ||
144 | <hex-integer> ::= "0" @("x"|"X"@) @<hex-digit-char>^+ | |
145 | ||
146 | <hex-digit-char> ::= <digit-char> | |
147 | \alt "A" | "B" | "C" | "D" | "E" | "F" | |
148 | \alt "a" | "b" | "c" | "d" | "e" | "f" | |
149 | \end{grammar} | |
150 | ||
151 | Sod understands only integers, not floating-point numbers; its integer syntax | |
152 | goes slightly beyond C in allowing a @`0o' prefix for octal and @`0b' for | |
153 | binary. However, length and signedness indicators are not permitted. | |
154 | ||
155 | \subsubsection{Punctuation} \label{sec:syntax.lex.punct} | |
156 | ||
157 | \begin{grammar} | |
158 | <punctuation> ::= any nonalphanumeric character other than "_", "\"" or "'" | |
159 | \end{grammar} | |
160 | ||
161 | \subsubsection{Comments} \label{sec:lex-comment} | |
162 | ||
163 | \begin{grammar} | |
164 | <comment> ::= <block-comment> | |
165 | \alt <line-comment> | |
166 | ||
167 | <block-comment> ::= | |
168 | "/*" | |
169 | @<not-star>^* @(@<star>^+ <not-star-or-slash> @<not-star>^*@)^* | |
170 | @<star>^* | |
171 | "*/" | |
172 | ||
173 | <star> ::= "*" | |
174 | ||
175 | <not-star> ::= any character other than "*" | |
176 | ||
177 | <not-star-or-slash> ::= any character other than "*" or "/" | |
178 | ||
179 | <line-comment> ::= "//" @<not-newline>^* <newline> | |
180 | ||
181 | <newline> ::= a newline character | |
182 | ||
183 | <not-newline> ::= any character other than newline | |
184 | \end{grammar} | |
185 | ||
186 | Comments are exactly as in C99: both traditional block comments `\texttt{/*} | |
187 | \dots\ \texttt{*/}' and \Cplusplus-style `\texttt{//} \dots' comments are | |
188 | permitted and ignored. | |
189 | ||
190 | \subsection{Special nonterminals} | |
191 | \label{sec:special-nonterminals} | |
192 | ||
193 | Aside from the lexical syntax presented above (\xref{sec:lexical-syntax}), | |
194 | two special nonterminals occur in the module syntax. | |
195 | ||
196 | \subsubsection{S-expressions} \label{sec:syntax-sexp} | |
197 | ||
198 | \begin{grammar} | |
199 | <s-expression> ::= an S-expression, as parsed by the Lisp reader | |
200 | \end{grammar} | |
201 | ||
202 | When an S-expression is expected, the Sod parser simply calls the host Lisp | |
203 | system's \textsf{read} function. Sod modules are permitted to modify the | |
204 | read table to extend the S-expression syntax. | |
205 | ||
206 | S-expressions are self-delimiting, so no end-marker is needed. | |
207 | ||
208 | \subsubsection{C fragments} \label{sec:syntax.lex.cfrag} | |
209 | ||
210 | \begin{grammar} | |
211 | <c-fragment> ::= a sequence of C tokens, with matching brackets | |
212 | \end{grammar} | |
213 | ||
214 | Sequences of C code are simply stored and written to the output unchanged | |
215 | during translation. They are read using a simple scanner which nonetheless | |
216 | understands C comments and string and character literals. | |
217 | ||
218 | A C fragment is terminated by one of a small number of delimiter characters | |
219 | determined by the immediately surrounding context -- usually a closing brace | |
220 | or bracket. The first such delimiter character which is not enclosed in | |
221 | brackets, braces or parenthesis ends the fragment. | |
222 | ||
223 | \subsection{Module syntax} \label{sec:syntax-module} | |
224 | ||
225 | \begin{grammar} | |
226 | <module> ::= @<definition>^* | |
227 | ||
228 | <definition> ::= <import-definition> | |
229 | \alt <load-definition> | |
230 | \alt <lisp-definition> | |
231 | \alt <code-definition> | |
232 | \alt <typename-definition> | |
233 | \alt <class-definition> | |
234 | \end{grammar} | |
235 | ||
236 | A module is the top-level syntactic item. A module consists of a sequence of | |
237 | definitions. | |
238 | ||
239 | \subsection{Simple definitions} \label{sec:syntax.defs} | |
240 | ||
241 | \subsubsection{Importing modules} \label{sec:syntax.defs.import} | |
242 | ||
243 | \begin{grammar} | |
244 | <import-definition> ::= "import" <string> ";" | |
245 | \end{grammar} | |
246 | ||
247 | The module named @<string> is processed and its definitions made available. | |
248 | ||
249 | A search is made for a module source file as follows. | |
250 | \begin{itemize} | |
251 | \item The module name @<string> is converted into a filename by appending | |
252 | @`.sod', if it has no extension already.\footnote{% | |
253 | Technically, what happens is \textsf{(merge-pathnames name (make-pathname | |
254 | :type "SOD" :case :common))}, so exactly what this means varies | |
255 | according to the host system.} % | |
256 | \item The file is looked for relative to the directory containing the | |
257 | importing module. | |
258 | \item If that fails, then the file is looked for in each directory on the | |
259 | module search path in turn. | |
260 | \item If the file still isn't found, an error is reported and the import | |
261 | fails. | |
262 | \end{itemize} | |
263 | At this point, if the file has previously been imported, nothing further | |
264 | happens.\footnote{% | |
265 | This check is done using \textsf{truename}, so it should see through simple | |
266 | tricks like symbolic links. However, it may be confused by fancy things | |
267 | like bind mounts and so on.} % | |
268 | ||
269 | Recursive imports, either direct or indirect, are an error. | |
270 | ||
271 | \subsubsection{Loading extensions} \label{sec:syntax.defs.load} | |
272 | ||
273 | \begin{grammar} | |
274 | <load-definition> ::= "load" <string> ";" | |
275 | \end{grammar} | |
276 | ||
277 | The Lisp file named @<string> is loaded and evaluated. | |
278 | ||
279 | A search is made for a Lisp source file as follows. | |
280 | \begin{itemize} | |
281 | \item The name @<string> is converted into a filename by appending @`.lisp', | |
282 | if it has no extension already.\footnote{% | |
283 | Technically, what happens is \textsf{(merge-pathnames name (make-pathname | |
284 | :type "LISP" :case :common))}, so exactly what this means varies | |
285 | according to the host system.} % | |
286 | \item A search is then made in the same manner as for module imports | |
287 | (\xref{sec:syntax-module}). | |
288 | \end{itemize} | |
289 | If the file is found, it is loaded using the host Lisp's \textsf{load} | |
290 | function. | |
291 | ||
292 | Note that Sod doesn't attempt to compile Lisp files, or even to look for | |
293 | existing compiled files. The right way to package a substantial extension to | |
294 | the Sod translator is to provide the extension as a standard ASDF system (or | |
295 | similar) and leave a dropping @"foo-extension.lisp" in the module path saying | |
296 | something like | |
297 | \begin{quote} | |
298 | \textsf{(asdf:load-system :foo-extension)} | |
299 | \end{quote} | |
300 | which will arrange for the extension to be compiled if necessary. | |
301 | ||
302 | (This approach means that the language doesn't need to depend on any | |
303 | particular system definition facility. It's bad enough already that it | |
304 | depends on Common Lisp.) | |
305 | ||
306 | \subsubsection{Lisp escapes} \label{sec:syntax.defs.lisp} | |
307 | ||
308 | \begin{grammar} | |
309 | <lisp-definition> ::= "lisp" <s-expression> ";" | |
310 | \end{grammar} | |
311 | ||
312 | The @<s-expression> is evaluated immediately. It can do anything it likes. | |
313 | ||
314 | \textbf{Warning!} This means that hostile Sod modules are a security hazard. | |
315 | Lisp code can read and write files, start other programs, and make network | |
316 | connections. Don't install Sod modules from sources that you don't | |
317 | trust.\footnote{% | |
318 | Presumably you were going to run the corresponding code at some point, so | |
319 | this isn't as unusually scary as it sounds. But please be careful.} % | |
320 | ||
321 | \subsubsection{Declaring type names} \label{sec:syntax.defs.typename} | |
322 | ||
323 | \begin{grammar} | |
324 | <typename-definition> ::= | |
325 | "typename" <identifier-list> ";" | |
326 | \end{grammar} | |
327 | ||
328 | Each @<identifier> is declared as naming a C type. This is important because | |
329 | the C type syntax -- which Sod uses -- is ambiguous, and disambiguation is | |
330 | done by distinguishing type names from other identifiers. | |
331 | ||
332 | Don't declare class names using @"typename"; use @"class" forward | |
333 | declarations instead. | |
334 | ||
335 | \subsection{Literal code} \label{sec:syntax-code} | |
336 | ||
337 | \begin{grammar} | |
338 | <code-definition> ::= | |
339 | "code" <identifier> ":" <identifier> @[<constraints>@] | |
340 | "{" <c-fragment> "}" | |
341 | ||
342 | <constraints> ::= "[" <constraint-list> "]" | |
343 | ||
344 | <constraint> ::= @<identifier>^+ | |
345 | \end{grammar} | |
346 | ||
347 | The @<c-fragment> will be output unchanged to one of the output files. | |
348 | ||
349 | The first @<identifier> is the symbolic name of an output file. Predefined | |
350 | output file names are @"c" and @"h", which are the implementation code and | |
351 | header file respectively; other output files can be defined by extensions. | |
352 | ||
353 | The second @<identifier> provides a name for the output item. Several C | |
354 | fragments can have the same name: they will be concatenated together in the | |
355 | order in which they were encountered. | |
356 | ||
357 | The @<constraints> provide a means for specifying where in the output file | |
358 | the output item should appear. (Note the two kinds of square brackets shown | |
359 | in the syntax: square brackets must appear around the constraints if they are | |
360 | present, but that they may be omitted.) Each comma-separated @<constraint> | |
361 | is a sequence of identifiers naming output items, and indicates that the | |
362 | output items must appear in the order given -- though the translator is free | |
363 | to insert additional items in between them. (The particular output items | |
364 | needn't be defined already -- indeed, they needn't be defined ever.) | |
365 | ||
366 | There is a predefined output item @"includes" in both the @"c" and @"h" | |
367 | output files which is a suitable place for inserting @"\#include" | |
368 | preprocessor directives in order to declare types and functions for use | |
369 | elsewhere in the generated output files. | |
370 | ||
371 | \subsection{Property sets} \label{sec:syntax.propset} | |
372 | ||
373 | \begin{grammar} | |
374 | <properties> ::= "[" <property-list> "]" | |
375 | ||
376 | <property> ::= <identifier> "=" <expression> | |
377 | \end{grammar} | |
378 | ||
379 | Property sets are a means for associating miscellaneous information with | |
380 | classes and related items. By using property sets, additional information | |
381 | can be passed to extensions without the need to introduce idiosyncratic | |
382 | syntax. | |
383 | ||
384 | A property has a name, given as an @<identifier>, and a value computed by | |
385 | evaluating an @<expression>. The value can be one of a number of types, | |
386 | though the only operators currently defined act on integer values only. | |
387 | ||
388 | \subsubsection{The expression evaluator} \label{sec:syntax.propset.expr} | |
389 | ||
390 | \begin{grammar} | |
391 | <expression> ::= <term> | <expression> "+" <term> | <expression> "-" <term> | |
392 | ||
393 | <term> ::= <factor> | <term> "*" <factor> | <term> "/" <factor> | |
394 | ||
395 | <factor> ::= <primary> | "+" <factor> | "-" <factor> | |
396 | ||
397 | <primary> ::= | |
398 | <integer-literal> | <string-literal> | <char-literal> | <identifier> | |
399 | \alt "?" <s-expression> | |
400 | \alt "(" <expression> ")" | |
401 | \end{grammar} | |
402 | ||
403 | The arithmetic expression syntax is simple and standard; there are currently | |
404 | no bitwise, logical, or comparison operators. | |
405 | ||
406 | A @<primary> expression may be a literal or an identifier. Note that | |
407 | identifiers stand for themselves: they \emph{do not} denote values. For more | |
408 | fancy expressions, the syntax | |
409 | \begin{quote} | |
410 | @"?" @<s-expression> | |
411 | \end{quote} | |
412 | causes the @<s-expression> to be evaluated using the Lisp \textsf{eval} | |
413 | function. | |
414 | %%% FIXME crossref to extension docs | |
415 | ||
416 | \subsection{C types} \label{sec:syntax.c-types} | |
417 | ||
418 | Sod's syntax for C types closely mirrors the standard C syntax. A C type has | |
419 | two parts: a sequence of @<declaration-specifier>s and a @<declarator>. In | |
420 | Sod, a type must contain at least one @<declaration-specifier> (i.e., | |
421 | `implicit @"int"' is forbidden), and storage-class specifiers are not | |
422 | recognized. | |
423 | ||
424 | \subsubsection{Declaration specifiers} \label{sec:syntax.c-types.declspec} | |
425 | ||
426 | \begin{grammar} | |
427 | <declaration-specifier> ::= <type-name> | |
428 | \alt "struct" <identifier> | "union" <identifier> | "enum" <identifier> | |
429 | \alt "void" | "char" | "int" | "float" | "double" | |
430 | \alt "short" | "long" | |
431 | \alt "signed" | "unsigned" | |
432 | \alt <qualifier> | |
433 | ||
434 | <qualifier> ::= "const" | "volatile" | "restrict" | |
435 | ||
436 | <type-name> ::= <identifier> | |
437 | \end{grammar} | |
438 | ||
439 | A @<type-name> is an identifier which has been declared as being a type name, | |
440 | using the @"typename" or @"class" definitions. | |
441 | ||
442 | Declaration specifiers may appear in any order. However, not all | |
443 | combinations are permitted. A declaration specifier must consist of zero or | |
444 | more @<qualifiers>, and one of the following, up to reordering. | |
445 | \begin{itemize} | |
446 | \item @<type-name> | |
447 | \item @"struct" @<identifier>, @"union" @<identifier>, @"enum" @<identifier> | |
448 | \item @"void" | |
449 | \item @"char", @"unsigned char", @"signed char" | |
450 | \item @"short", @"unsigned short", @"signed short" | |
451 | \item @"short int", @"unsigned short int", @"signed short int" | |
452 | \item @"int", @"unsigned int", @"signed int", @"unsigned", @"signed" | |
453 | \item @"long", @"unsigned long", @"signed long" | |
454 | \item @"long int", @"unsigned long int", @"signed long int" | |
455 | \item @"long long", @"unsigned long long", @"signed long long" | |
456 | \item @"long long int", @"unsigned long long int", @"signed long long int" | |
457 | \item @"float", @"double", @"long double" | |
458 | \end{itemize} | |
459 | All of these have their usual C meanings. | |
460 | ||
461 | \subsubsection{Declarators} \label{sec:syntax.c-types.declarator} | |
462 | ||
463 | \begin{grammar} | |
464 | <declarator>$[k]$ ::= @<pointer>^* <primary-declarator>$[k]$ | |
465 | ||
466 | <primary-declarator>$[k]$ ::= $k$ | |
467 | \alt "(" <primary-declarator>$[k]$ ")" | |
468 | \alt <primary-declarator>$[k]$ @<declarator-suffix>^* | |
469 | ||
470 | <pointer> ::= "*" @<qualifier>^* | |
471 | ||
472 | <declarator-suffix> ::= "[" <c-fragment> "]" | |
473 | \alt "(" <arguments> ")" | |
474 | ||
475 | <arguments> ::= $\epsilon$ | "..." | |
476 | \alt <argument-list> @["," "..."@] | |
477 | ||
478 | <argument> ::= @<declaration-specifier>^+ <argument-declarator> | |
479 | ||
480 | <argument-declarator> ::= <declarator>@[<identifier> @! $\epsilon$@] | |
481 | ||
482 | <simple-declarator> ::= <declarator>@[<identifier>@] | |
483 | ||
484 | <dotted-name> ::= <identifier> "." <identifier> | |
485 | ||
486 | <dotted-declarator> ::= <declarator>@[<dotted-name>@] | |
487 | \end{grammar} | |
488 | ||
489 | The declarator syntax is taken from C, but with some differences. | |
490 | \begin{itemize} | |
491 | \item Array dimensions are uninterpreted @<c-fragments>, terminated by a | |
492 | closing square bracket. This allows array dimensions to contain arbitrary | |
493 | constant expressions. | |
494 | \item A declarator may have either a single @<identifier> at its centre or a | |
495 | pair of @<identifier>s separated by a @`.'; this is used to refer to | |
496 | slots or messages defined in superclasses. | |
497 | \end{itemize} | |
498 | The remaining differences are (I hope) a matter of presentation rather than | |
499 | substance. | |
500 | ||
501 | \subsection{Defining classes} \label{sec:syntax.class} | |
502 | ||
503 | \begin{grammar} | |
504 | <class-definition> ::= <class-forward-declaration> | |
505 | \alt <full-class-definition> | |
506 | \end{grammar} | |
507 | ||
508 | \subsubsection{Forward declarations} \label{sec:class.class.forward} | |
509 | ||
510 | \begin{grammar} | |
511 | <class-forward-declaration> ::= "class" <identifier> ";" | |
512 | \end{grammar} | |
513 | ||
514 | A @<class-forward-declaration> informs Sod that an @<identifier> will be used | |
515 | to name a class which is currently undefined. Forward declarations are | |
516 | necessary in order to resolve certain kinds of circularity. For example, | |
517 | \begin{listing} | |
518 | class Sub; | |
519 | ||
520 | class Super : SodObject { | |
521 | Sub *sub; | |
522 | }; | |
523 | ||
524 | class Sub : Super { | |
525 | /* ... */ | |
526 | }; | |
527 | \end{listing} | |
528 | ||
529 | \subsubsection{Full class definitions} \label{sec:class.class.full} | |
530 | ||
531 | \begin{grammar} | |
532 | <full-class-definition> ::= | |
533 | @[<properties>@] | |
534 | "class" <identifier> ":" <identifier-list> | |
535 | "{" @<class-item>^* "}" | |
536 | ||
537 | <class-item> ::= <slot-item> ";" | |
538 | \alt <message-item> | |
539 | \alt <method-item> | |
540 | \alt <initializer-item> ";" | |
541 | \end{grammar} | |
542 | ||
543 | A full class definition provides a complete description of a class. | |
544 | ||
545 | The first @<identifier> gives the name of the class. It is an error to | |
546 | give the name of an existing class (other than a forward-referenced class), | |
547 | or an existing type name. It is conventional to give classes `MixedCase' | |
548 | names, to distinguish them from other kinds of identifiers. | |
549 | ||
550 | The @<identifier-list> names the direct superclasses for the new class. It | |
551 | is an error if any of these @<identifier>s does not name a defined class. | |
552 | ||
553 | The @<properties> provide additional information. The standard class | |
554 | properties are as follows. | |
555 | \begin{description} | |
556 | \item[@"lisp_class"] The name of the Lisp class to use within the translator | |
557 | to represent this class. The property value must be an identifier; the | |
558 | default is @"sod_class". Extensions may define classes with additional | |
559 | behaviour, and may recognize additional class properties. | |
560 | \item[@"metaclass"] The name of the Sod metaclass for this class. In the | |
561 | generated code, a class is itself an instance of another class -- its | |
562 | \emph{metaclass}. The metaclass defines which slots the class will have, | |
563 | which messages it will respond to, and what its behaviour will be when it | |
564 | receives them. The property value must be an identifier naming a defined | |
565 | subclass of @"SodClass". The default metaclass is @"SodClass". | |
566 | %%% FIXME xref to theory | |
567 | \item[@"nick"] A nickname for the class, to be used to distinguish it from | |
568 | other classes in various limited contexts. The property value must be an | |
569 | identifier; the default is constructed by forcing the class name to | |
570 | lower-case. | |
571 | \end{description} | |
572 | ||
573 | The class body consists of a sequence of @<class-item>s enclosed in braces. | |
574 | These items are discussed on the following sections. | |
575 | ||
576 | \subsubsection{Slot items} \label{sec:sntax.class.slot} | |
577 | ||
578 | \begin{grammar} | |
579 | <slot-item> ::= | |
580 | @[<properties>@] | |
581 | @<declaration-specifier>^+ <init-declarator-list> | |
582 | ||
583 | <init-declarator> ::= <declarator> @["=" <initializer>@] | |
584 | \end{grammar} | |
585 | ||
586 | A @<slot-item> defines one or more slots. All instances of the class and any | |
587 | subclass will contain these slot, with the names and types given by the | |
588 | @<declaration-specifiers> and the @<declarators>. Slot declarators may not | |
589 | contain qualified identifiers. | |
590 | ||
591 | It is not possible to declare a slot with function type: such an item is | |
592 | interpreted as being a @<message-item> or @<method-item>. Pointers to | |
593 | functions are fine. | |
594 | ||
595 | An @<initializer>, if present, is treated as if a separate | |
596 | @<initializer-item> containing the slot name and initializer were present. | |
597 | For example, | |
598 | \begin{listing} | |
599 | [nick = eg] | |
600 | class Example : Super { | |
601 | int foo = 17; | |
602 | }; | |
603 | \end{listing} | |
604 | means the same as | |
605 | \begin{listing} | |
606 | [nick = eg] | |
607 | class Example : Super { | |
608 | int foo; | |
609 | eg.foo = 17; | |
610 | }; | |
611 | \end{listing} | |
612 | ||
613 | \subsubsection{Initializer items} \label{sec:syntax.class.init} | |
614 | ||
615 | \begin{grammar} | |
616 | <initializer-item> ::= @["class"@] <slot-initializer-list> | |
617 | ||
618 | <slot-initializer> ::= <qualified-identifier> "=" <initializer> | |
619 | ||
620 | <initializer> :: "{" <c-fragment> "}" | <c-fragment> | |
621 | \end{grammar} | |
622 | ||
623 | An @<initializer-item> provides an initial value for one or more slots. If | |
624 | prefixed by @"class", then the initial values are for class slots (i.e., | |
625 | slots of the class object itself); otherwise they are for instance slots. | |
626 | ||
627 | The first component of the @<qualified-identifier> must be the nickname of | |
628 | one of the class's superclasses (including itself); the second must be the | |
629 | name of a slot defined in that superclass. | |
630 | ||
631 | The initializer has one of two forms. | |
632 | \begin{itemize} | |
633 | \item A @<c-fragment> enclosed in braces denotes an aggregate initializer. | |
634 | This is suitable for initializing structure, union or array slots. | |
635 | \item A @<c-fragment> \emph{not} beginning with an open brace is a `bare' | |
636 | initializer, and continues until the next @`,' or @`;' which is not within | |
637 | nested brackets. Bare initializers are suitable for initializing scalar | |
638 | slots, such as pointers or integers, and strings. | |
639 | \end{itemize} | |
640 | ||
641 | \subsubsection{Message items} \label{sec:syntax.class.message} | |
642 | ||
643 | \begin{grammar} | |
644 | <message-item> ::= | |
645 | @[<properties>@] | |
646 | @<declaration-specifier>^+ <declarator> @[<method-body>@] | |
647 | \end{grammar} | |
648 | ||
649 | \subsubsection{Method items} \label{sec:syntax.class.method} | |
650 | ||
651 | \begin{grammar} | |
652 | <method-item> ::= | |
653 | @[<properties>@] | |
654 | @<declaration-specifier>^+ <declarator> <method-body> | |
655 | ||
656 | <method-body> ::= "{" <c-fragment> "}" | "extern" ";" | |
657 | \end{grammar} | |
658 | ||
659 | ||
660 | %%%----- That's all, folks -------------------------------------------------- | |
661 | ||
662 | %%% Local variables: | |
663 | %%% mode: LaTeX | |
664 | %%% TeX-master: "sod.tex" | |
665 | %%% TeX-PDF-mode: t | |
666 | %%% End: |