1XS::Parse::Keyword(3) User Contributed Perl DocumentationXS::Parse::Keyword(3)
2
6 "XS::Parse::Keyword" - XS functions to assist in parsing keyword syntax
7
9 This module provides some XS functions to assist in writing syntax
10 modules that provide new perl-visible syntax, primarily for authors of
11 keyword plugins using the "PL_keyword_plugin" hook mechanism. It is
12 unlikely to be of much use to anyone else; and highly unlikely to be
13 any use when writing perl code using these. Unless you are writing a
14 keyword plugin using XS, this module is not for you.
15 This module is also currently experimental, and the design is still
17 evolving and subject to change. Later versions may break ABI
18 compatibility, requiring changes or at least a rebuild of any module
19 that depends on it.
20
22 boot_xs_parse_keyword
23 void boot_xs_parse_keyword(double ver);
24 Call this function from your "BOOT" section in order to initialise the
26 module and parsing hooks.
27 ver should either be 0 or a decimal number for the module version
29 requirement; e.g.
30 boot_xs_parse_keyword(0.14);
32 register_xs_parse_keyword
34 void register_xs_parse_keyword(const char *keyword,
35 const struct XSParseKeywordHooks *hooks, void *hookdata);
36 This function installs a set of parsing hooks to be associated with the
38 given keyword. Such a keyword will then be handled automatically by a
39 keyword parser installed by "XS::Parse::Keyword" itself.
40
42 The "XSParseKeywordHooks" structure provides the following hook stages,
43 which are invoked in the given order.
44 flags
46 The following flags are defined:
47 "XPK_FLAG_EXPR"
49 The parse or build function is expected to return
50 "KEYWORD_PLUGIN_EXPR".
51 "XPK_FLAG_STMT"
53 The parse or build function is expected to return
54 "KEYWORD_PLUGIN_STMT".
55 These two flags are largely for the benefit of giving static
57 information at registration time to assist static parsing or other
58 related tasks to know what kind of grammatical element this keyword
59 will produce.
60 "XPK_FLAG_AUTOSEMI"
62 The syntax forms a complete statement, which should be followed by
63 a statement separator semicolon (";"). This semicolon is optional
64 at the end of a block.
65 The semicolon, if present, will be consumed automatically.
67 The "permit" Stage
69 const char *permit_hintkey;
70 bool (*permit) (pTHX_ void *hookdata);
71 Called by the installed keyword parser hook which is used to handle
73 keywords registered by "register_xs_parse_keyword".
74 As a shortcut for the common case, the "permit_hintkey" may point to a
76 string to look up from the hints hash. If the given key name is not
77 found in the hints hash then the keyword is not permitted. If the key
78 is present then the "permit" function is invoked as normal.
79 If not rejected by a hint key that was not found in the hints hash, the
81 function part of the stage is called next and should inspect whether
82 the keyword is permitted at this time perhaps by inspecting other
83 lexical clues, and return true only if the keyword is permitted.
84 Both the string and the function are optional. Either or both may be
86 present. If neither is present then the keyword is always permitted -
87 which is likely not what you wanted to do.
88 The "check" Stage
90 void (*check)(pTHX_ void *hookdata);
91 Invoked once the keyword has been permitted. If present, this hook
93 function can check the surrounding lexical context, state, or other
94 information and throw an exception if it is unhappy that the keyword
95 should apply in this position.
96 The "parse" Stage
98 This stage is invoked once the keyword has been checked, and actually
99 parses the incoming text into an optree. It is implemented by calling
100 the first of the following function pointers which is not NULL. The
101 invoked function may optionally build an optree to represent the parsed
102 syntax, and place it into the variable addressed by "out". If it does
103 not, then a simple "OP_NULL" will be constructed in its place.
104 "lex_read_space()" is called both before and after this stage is
106 invoked, so in many simple cases the hook function itself does not need
107 to bother with it.
108 int (*parse)(pTHX_ OP **out, void *hookdata);
110 If present, this should consume text from the parser buffer by invoking
112 "lex_*" or "parse_*" functions and eventually return a
113 "KEYWORD_PLUGIN_*" result value.
114 This is the most generic and powerful of the options, but requires the
116 most amount of implementation work.
117 int (*build)(pTHX_ OP **out, XSParseKeywordPiece *args[], size_t nargs, void *hookdata);
119 If "parse" is not present, this is called instead after parsing a
121 sequence of arguments, of types given by the pieces field; which should
122 be a zero- terminated array of piece types.
123 This alternative is somewhat less generic and powerful than providing
125 "parse" yourself, but involves much less parsing work and is shorter
126 and easier to implement.
127 int (*build1)(pTHX_ OP **out, XSParseKeywordPiece *arg0, void *hookdata);
129 If neither "parse" nor "build" are present, this is called as a simpler
131 variant of "build" when only a single argument is required. It takes
132 its type from the "piece1" field instead.
133
135 When using the "build" or "build1" alternatives for the "parse" phase,
136 the actual syntax is parsed automatically by this module, according to
137 the specification given by the pieces or piece1 field. The result of
138 that parsing step is placed into the args or arg0 parameter to the
139 invoked function, using a "struct" type consisting of the following
140 fields:
141 typedef struct
143 union {
144 OP *op;
145 CV *cv;
146 SV *sv;
147 int i;
148 struct {
149 SV *name;
150 SV *value;
151 } attr;
152 PADOFFSET padix;
153 struct XSParseInfixInfo *infix;
154 };
155 int line;
156 } XSParseKeywordPiece;
157 Which field of the anonymous union is set depends on the type of the
159 piece. The line field contains the line number of the source file
160 where parsing of that piece began.
161 Some piece types are "atomic", whose definition is self-contained.
163 Others are structural, defined in terms of inner pieces. Together these
164 form an entire tree-shaped definition of the syntax that the keyword
165 expects to find.
166 Atomic types generally provide exactly one argument into the list of
168 args (with the exception of literal matches, which do not provide
169 anything). Structural types may provide an initial argument
170 themselves, followed by a list of the values of each sub-piece they
171 contained inside them. Thus, while the data structure defining the
172 syntax shape is a tree, the argument values it parses into is passed as
173 a flat array to the "build" function.
174 Some structural types need to be able to determine whether or not
176 syntax relating some optional part of them is present in the incoming
177 source text. In this case, the pieces relating to those optional parts
178 must support "probing". This ability is also noted below.
179 The type of each piece should be one of the following macro values.
181 XPK_BLOCK
183 atomic, can probe, emits op.
184 XPK_BLOCK
186 A brace-delimited block of code is expected, passed as an optree in the
188 op field. This will be parsed as a block within the current function
189 scope.
190 This can be probed by checking for the presence of an open-brace ("{")
192 character.
193 Be careful defining grammars with this because an open-brace is also a
195 valid character to start a term expression, for example. Given a choice
196 between "XPK_BLOCK" and "XPK_TERMEXPR", either of them could try to
197 consume such code as
198 { 123, 456 }
200 XPK_BLOCK_VOIDCTX, XPK_BLOCK_SCALARCTX, XPK_BLOCK_LISTCTX
202 Variants of "XPK_BLOCK" which wrap a void, scalar or list-context scope
203 around the block.
204 XPK_PREFIXED_BLOCK
206 structural, emits op.
207 XPK_PREFIXED_BLOCK(pieces ...)
209 Some pieces are expected, followed by a brace-delimited block of code,
211 which is passed as an optree in the op field. The prefix pieces are
212 parsed first, and their results are passed before the block itself.
213 The entire sequence, including the prefix items, is contained within a
215 pair of "block_start()" / "block_end()" calls. This permits the prefix
216 pieces to introduce new items into the lexical scope of the block - for
217 example by the use of "XPK_LEXVAR_MY".
218 A call to "intro_my()" is automatically made at the end of the prefix
220 pieces, before the block itself is parsed, ensuring any new lexical
221 variables are now visible.
222 In addition, the following extra piece types are recognised here:
224 XPK_SETUP
226 void setup(pTHX_ void *hookdata);
227 XPK_SETUP(&setup)
229 atomic, emits nothing.
231 This piece type runs a function given by pointer. Typically this
233 function may be used to introduce new lexical state into the
234 parser, or in some other way have some side-effect on the parsing
235 context of the block to be parsed.
236 XPK_PREFIXED_BLOCK_ENTERLEAVE
238 A variant of "XPK_PREFIXED_BLOCK" which additionally wraps the entire
239 parsing operation, including the "block_start()", "block_end()" and any
240 calls to "XPK_SETUP" functions, within a "ENTER"/"LEAVE" pair.
241 This should not make a difference to the standard parser pieces
243 provided here, but may be useful behaviour for the code in the setup
244 function, especially if it wishes to modify parser state and use the
245 savestack to ensure it is restored again when parsing has finished.
246 XPK_ANONSUB
248 atomic, emits op.
249 A brace-delimited block of code is expected, and assembled into the
251 body of a new anonymous subroutine. This will be passed as a protosub
252 CV in the cv field.
253 XPK_TERMEXPR
255 atomic, emits op.
256 XPK_TERMEXPR
258 A term expression is expected, parsed using "parse_termexpr()", and
260 passed as an optree in the op field.
261 XPK_TERMEXPR_VOIDCTX, XPK_TERMEXPR_SCALARCTX
263 Variants of "XPK_TERMEXPR" which puts the expression in void or scalar
264 context.
265 XPK_LISTEXPR
267 atomic, emits op.
268 XPK_LISTEXPR
270 A list expression is expected, parsed using "parse_listexpr()", and
272 passed as an optree in the op field.
273 XPK_LISTEXPR_LISTCTX
275 Variant of "XPK_LISTEXPR" which puts the expression in list context.
276 XPK_IDENT, XPK_IDENT_OPT
278 atomic, can probe, emits sv.
279 A bareword identifier name is expected, and passed as an SV containing
281 a PV in the sv field. An identifier is not permitted to contain a
282 double colon ("::").
283 The "_OPT"-suffixed version is optional; if no identifier is found then
285 sv is set to "NULL".
286 XPK_PACKAGENAME, XPK_PACKAGENAME_OPT
288 atomic, can probe, emits sv.
289 A bareword package name is expected, and passed as an SV containing a
291 PV in the sv field. A package name is similar to an identifier, except
292 it permits double colons in the middle.
293 The "_OPT"-suffixed version is optional; if no package name is found
295 then sv is set to "NULL".
296 XPK_LEXVARNAME
298 atomic, emits sv.
299 XPK_LEXVARNAME(kind)
301 A lexical variable name is expected, and passed as an SV containing a
303 PV in the sv field. The "kind" argument specifies what kinds of
304 variable are permitted, and should be a bitmask of one or more bits
305 from "XPK_LEXVAR_SCALAR", "XPK_LEXVAR_ARRAY" and "XPK_LEXVAR_HASH". A
306 convenient shortcut "XPK_LEXVAR_ANY" permits all three.
307 XPK_ATTRIBUTES
309 atomic, emits i followed by more args.
310 A list of ":"-prefixed attributes is expected, in the same format as
312 sub or variable attributes. An optional leading ":" indicates the
313 presence of attributes, then one or more of them are parsed. Attributes
314 may be optionally separated by additional ":"s, but this is not
315 required.
316 Each attribute is expected to be an identifier name, followed by an
318 optional value wrapped in parentheses. Whitespace is NOT permitted
319 between the name and value, as per standard Perl parsing rules.
320 :attrname
322 :attrname(value)
323 The i field indicates how many attributes were found. That number of
325 additional arguments are then passed, each containing two SVs in the
326 attr.name and attr.value fields. This number may be zero.
327 It is not an error for there to be no attributes present, or for the
329 optional colon to be missing. In this case i will be set to zero.
330 XPK_VSTRING, XPK_VSTRING_OPT
332 atomic, can probe, emits sv.
333 A version string is expected, of the form "v1.234" including the
335 leading "v" character. It is passed as a version SV object in the sv
336 field.
337 The "_OPT"-suffixed version is optional; if no version string is found
339 then sv is set to "NULL".
340 XPK_LEXVAR_MY
342 atomic, emits padix.
343 XPK_LEXVAR_MY(kind)
345 A lexical variable name is expected, added to the current pad as if
347 specified in a "my" expression, and passed as the pad index in the
348 padix field.
349 The "kind" argument specifies what kinds of variable are permitted, as
351 per "XPK_LEXVARNAME".
352 XPK_COMMA, XPK_COLON, XPK_EQUALS
354 atomic, can probe, emits nothing.
355 A literal character (",", ":" or "=") is expected. No argument value is
357 passed.
358 XPK_INFIX_*
360 atomic, can probe, emits infix.
361 An infix operator as recognised by XS::Parse::Infix. The returned
363 pointer points to a structure allocated by "XS::Parse::Infix"
364 describing the operator.
365 Various versions of the macro are provided, each using a different
367 selection filter to choose certain available infix operators:
368 XPK_INFIX_RELATION # any relational operator
370 XPK_INFIX_EQUALITY # an equality operator like `==` or `eq`
371 XPK_INFIX_MATCH_NOSMART # any sort of "match"-like operator, except smartmatch
372 XPK_INFIX_MATCH_SMART # XPK_INFIX_MATCH_NOSMART plus smartmatch
373 XPK_LITERAL
375 atomic, can probe, emits nothing.
376 XPK_LITERAL("literal")
378 A literal string match is expected. No argument value is passed.
380 This form should generally be avoided if at all possible, because it is
382 very easy to abuse to make syntaxes which confuse humans and code tools
383 alike. Generally it is best reserved just for the first component of a
384 "XPK_OPTIONAL" or "XPK_REPEATED" sequence, to provide a "secondary
385 keyword" that such a repeated item can look out for.
386 This was previously called "XPK_STRING", and is provided as a synonym
388 for back-compatibility but new code should use this new name instead.
389 XPK_SEQUENCE
391 structural, might support probe, emits nothing.
392 XPK_SEQUENCE(pieces ...)
394 A structural type which contains a number of pieces. This is normally
396 equivalent to simply placing the pieces in sequence inside their own
397 container, but it is useful inside "XPK_CHOICE" or "XPK_TAGGEDCHOICE".
398 An "XPK_SEQUENCE" supports probe if its first contained piece does;
400 i.e. is transparent to probing.
401 XPK_OPTIONAL
403 structural, emits i.
404 XPK_OPTIONAL(pieces ...)
406 A structural type which may expects to find its contained pieces, or is
408 happy not to. This will pass an argument whose i field contains either
409 1 or 0, depending whether the contents were found. The first piece type
410 within must support probe.
411 XPK_REPEATED
413 structural, emits i.
414 XPK_REPEATED(pieces ...)
416 A structural type which expects to find zero or more repeats of its
418 contained pieces. This will pass an argument whose i field contains the
419 count of the number of repeats it found. The first piece type within
420 must support probe.
421 XPK_CHOICE
423 structural, can probe, emits i.
424 XPK_CHOICE(options ...)
426 A structural type which expects to find one of a number of alternative
428 options. An ordered list of types is provided, all of which must
429 support probe. This will pass an argument whose i field gives the index
430 of the first choice that was accepted. The first option takes the value
431 0.
432 As each of the options is interpreted as an alternative, not a
434 sequence, you should use "XPK_SEQUENCE" if a sequence of multiple items
435 should be considered as a single alternative.
436 It is not an error if no choice matches. At that point, the i field
438 will be set to -1.
439 If you require a failure message in this case, set the final choice to
441 be of type "XPK_FAILURE". This will cause an error message to be
442 printed instead.
443 XPK_FAILURE("message string")
445 XPK_TAGGEDCHOICE
447 structural, can probe, emits i.
448 XPK_TAGGEDCHOICE(choice, tag, ...)
450 A structural type similar to "XPK_CHOICE", except that each choice type
452 is followed by an element of type "XPK_TAG" which gives an integer. It
453 is that integer value, rather than the positional index of the choice
454 within the list, which is passed in the i field.
455 XPK_TAG(value)
457 As each of the options is interpreted as an alternative, not a
459 sequence, you should use "XPK_SEQUENCE" if a sequence of multiple items
460 should be considered as a single alternative.
461 XPK_COMMALIST
463 structural, might support probe, emits i.
464 XPK_COMMALIST(pieces ...)
466 A structural type which expects to find one or more repeats of its
468 contained pieces, separated by literal comma (",") characters. This is
469 somewhat similar to "XPK_REPEATED", except that it needs at least one
470 copy, needs commas between its items, but does not require that the
471 first contained piece support probe (the comma itself is sufficient to
472 indicate a repeat).
473 An "XPK_COMMALIST" supports probe if its first contained piece does;
475 i.e. is transparent to probing.
476 XPK_PARENSCOPE
478 structural, can probe, emits nothing.
479 XPK_PARENSCOPE(pieces ...)
481 A structural type which expects to find a sequence of pieces, all
483 contained in parentheses as "( ... )". This will pass no extra
484 arguments.
485 XPK_BRACKETSCOPE
487 structural, can probe, emits nothing.
488 XPK_BRACKETSCOPE(pieces ...)
490 A structural type which expects to find a sequence of pieces, all
492 contained in square brackets as "[ ... ]". This will pass no extra
493 arguments.
494 XPK_BRACESCOPE
496 structural, can probe, emits nothing.
497 XPK_BRACESCOPE(pieces ...)
499 A structural type which expects to find a sequence of pieces, all
501 contained in braces as "{ ... }". This will pass no extra arguments.
502 Note that this is not necessary to use with "XPK_BLOCK" or
504 "XPK_ANONSUB"; those will already consume a set of braces. This is
505 intended for special constrained syntax that should not just accept an
506 arbitrary block.
507 XPK_CHEVRONSCOPE
509 structural, can probe, emits nothing.
510 XPK_CHEVRONSCOPE(pieces ...)
512 A structural type which expects to find a sequence of pieces, all
514 contained in angle brackets as "< ... >". This will pass no extra
515 arguments.
516 Remember that expressions like "a > b" are valid term expressions, so
518 the contents of this scope shouldn't allow arbitrary expressions or the
519 closing bracket will be ambiguous.
520 XPK_PARENSCOPE_OPT, XPK_BRACKETSCOPE_OPT, XPK_BRACESCOPE_OPT,
522 XPK_CHEVRONSCOPE_OPT
523 structural, can probe, emits i.
524 XPK_PARENSCOPE_OPT(pieces ...)
526 XPK_BRACKETSCOPE_OPT(pieces ...)
527 XPK_BRACESCOPE_OPT(pieces ...)
528 XPK_CHEVERONSCOPE_OPT(pieces ...)
529 Each of the four "XPK_...SCOPE" macros above has an optional variant,
531 whose name is suffixed by "_OPT". These pass an argument whose i field
532 is either true or false, indicating whether the scope was found,
533 followed by the values from the scope itself.
534 This is a convenient shortcut to nesting the scope within a
536 "XPK_OPTIONAL" macro.
537
539 Paul Evans <leonerd@leonerd.org.uk>
540perl v5.34.0 2021-10-12 XS::Parse::Keyword(3)