Provided by: libxs-parse-keyword-perl_0.25-1_amd64 
NAME
"XS::Parse::Keyword" - XS functions to assist in parsing keyword syntax
DESCRIPTION
This module provides some XS functions to assist in writing syntax modules that provide
new perl-visible syntax, primarily for authors of keyword plugins using the
"PL_keyword_plugin" hook mechanism. It is unlikely to be of much use to anyone else; and
highly unlikely to be any use when writing perl code using these. Unless you are writing a
keyword plugin using XS, this module is not for you.
This module is also currently experimental, and the design is still evolving and subject
to change. Later versions may break ABI compatibility, requiring changes or at least a
rebuild of any module that depends on it.
XS FUNCTIONS
boot_xs_parse_keyword
void boot_xs_parse_keyword(double ver);
Call this function from your "BOOT" section in order to initialise the module and parsing
hooks.
ver should either be 0 or a decimal number for the module version requirement; e.g.
boot_xs_parse_keyword(0.14);
register_xs_parse_keyword
void register_xs_parse_keyword(const char *keyword,
const struct XSParseKeywordHooks *hooks, void *hookdata);
This function installs a set of parsing hooks to be associated with the given keyword.
Such a keyword will then be handled automatically by a keyword parser installed by
"XS::Parse::Keyword" itself.
PARSE HOOKS
The "XSParseKeywordHooks" structure provides the following hook stages, which are invoked
in the given order.
flags
The following flags are defined:
"XPK_FLAG_EXPR"
The parse or build function is expected to return "KEYWORD_PLUGIN_EXPR".
"XPK_FLAG_STMT"
The parse or build function is expected to return "KEYWORD_PLUGIN_STMT".
These two flags are largely for the benefit of giving static information at
registration time to assist static parsing or other related tasks to know what kind of
grammatical element this keyword will produce.
"XPK_FLAG_AUTOSEMI"
The syntax forms a complete statement, which should be followed by a statement
separator semicolon (";"). This semicolon is optional at the end of a block.
The semicolon, if present, will be consumed automatically.
The "permit" Stage
const char *permit_hintkey;
bool (*permit) (pTHX_ void *hookdata);
Called by the installed keyword parser hook which is used to handle keywords registered by
"register_xs_parse_keyword".
As a shortcut for the common case, the "permit_hintkey" may point to a string to look up
from the hints hash. If the given key name is not found in the hints hash then the keyword
is not permitted. If the key is present then the "permit" function is invoked as normal.
If not rejected by a hint key that was not found in the hints hash, the function part of
the stage is called next and should inspect whether the keyword is permitted at this time
perhaps by inspecting other lexical clues, and return true only if the keyword is
permitted.
Both the string and the function are optional. Either or both may be present. If neither
is present then the keyword is always permitted - which is likely not what you wanted to
do.
The "check" Stage
void (*check)(pTHX_ void *hookdata);
Invoked once the keyword has been permitted. If present, this hook function can check the
surrounding lexical context, state, or other information and throw an exception if it is
unhappy that the keyword should apply in this position.
The "parse" Stage
This stage is invoked once the keyword has been checked, and actually parses the incoming
text into an optree. It is implemented by calling the first of the following function
pointers which is not NULL. The invoked function may optionally build an optree to
represent the parsed syntax, and place it into the variable addressed by "out". If it does
not, then a simple "OP_NULL" will be constructed in its place.
"lex_read_space()" is called both before and after this stage is invoked, so in many
simple cases the hook function itself does not need to bother with it.
int (*parse)(pTHX_ OP **out, void *hookdata);
If present, this should consume text from the parser buffer by invoking "lex_*" or
"parse_*" functions and eventually return a "KEYWORD_PLUGIN_*" result value.
This is the most generic and powerful of the options, but requires the most amount of
implementation work.
int (*build)(pTHX_ OP **out, XSParseKeywordPiece *args[], size_t nargs, void *hookdata);
If "parse" is not present, this is called instead after parsing a sequence of arguments,
of types given by the pieces field; which should be a zero- terminated array of piece
types.
This alternative is somewhat less generic and powerful than providing "parse" yourself,
but involves much less parsing work and is shorter and easier to implement.
int (*build1)(pTHX_ OP **out, XSParseKeywordPiece *arg0, void *hookdata);
If neither "parse" nor "build" are present, this is called as a simpler variant of "build"
when only a single argument is required. It takes its type from the "piece1" field
instead.
PIECES AND PIECE TYPES
When using the "build" or "build1" alternatives for the "parse" phase, the actual syntax
is parsed automatically by this module, according to the specification given by the pieces
or piece1 field. The result of that parsing step is placed into the args or arg0 parameter
to the invoked function, using a "struct" type consisting of the following fields:
typedef struct
union {
OP *op;
CV *cv;
SV *sv;
int i;
struct {
SV *name;
SV *value;
} attr;
PADOFFSET padix;
struct XSParseInfixInfo *infix;
};
int line;
} XSParseKeywordPiece;
Which field of the anonymous union is set depends on the type of the piece. The line
field contains the line number of the source file where parsing of that piece began.
Some piece types are "atomic", whose definition is self-contained. Others are structural,
defined in terms of inner pieces. Together these form an entire tree-shaped definition of
the syntax that the keyword expects to find.
Atomic types generally provide exactly one argument into the list of args (with the
exception of literal matches, which do not provide anything). Structural types may
provide an initial argument themselves, followed by a list of the values of each sub-piece
they contained inside them. Thus, while the data structure defining the syntax shape is a
tree, the argument values it parses into is passed as a flat array to the "build"
function.
Some structural types need to be able to determine whether or not syntax relating some
optional part of them is present in the incoming source text. In this case, the pieces
relating to those optional parts must support "probing". This ability is also noted
below.
The type of each piece should be one of the following macro values.
XPK_BLOCK
atomic, can probe, emits op.
XPK_BLOCK
A brace-delimited block of code is expected, passed as an optree in the op field. This
will be parsed as a block within the current function scope.
This can be probed by checking for the presence of an open-brace ("{") character.
Be careful defining grammars with this because an open-brace is also a valid character to
start a term expression, for example. Given a choice between "XPK_BLOCK" and
"XPK_TERMEXPR", either of them could try to consume such code as
{ 123, 456 }
XPK_BLOCK_VOIDCTX, XPK_BLOCK_SCALARCTX, XPK_BLOCK_LISTCTX
Variants of "XPK_BLOCK" which wrap a void, scalar or list-context scope around the block.
XPK_PREFIXED_BLOCK
structural, emits op.
XPK_PREFIXED_BLOCK(pieces ...)
Some pieces are expected, followed by a brace-delimited block of code, which is passed as
an optree in the op field. The prefix pieces are parsed first, and their results are
passed before the block itself.
The entire sequence, including the prefix items, is contained within a pair of
"block_start()" / "block_end()" calls. This permits the prefix pieces to introduce new
items into the lexical scope of the block - for example by the use of "XPK_LEXVAR_MY".
A call to "intro_my()" is automatically made at the end of the prefix pieces, before the
block itself is parsed, ensuring any new lexical variables are now visible.
In addition, the following extra piece types are recognised here:
XPK_SETUP
void setup(pTHX_ void *hookdata);
XPK_SETUP(&setup)
atomic, emits nothing.
This piece type runs a function given by pointer. Typically this function may be used
to introduce new lexical state into the parser, or in some other way have some side-
effect on the parsing context of the block to be parsed.
XPK_PREFIXED_BLOCK_ENTERLEAVE
A variant of "XPK_PREFIXED_BLOCK" which additionally wraps the entire parsing operation,
including the "block_start()", "block_end()" and any calls to "XPK_SETUP" functions,
within a "ENTER"/"LEAVE" pair.
This should not make a difference to the standard parser pieces provided here, but may be
useful behaviour for the code in the setup function, especially if it wishes to modify
parser state and use the savestack to ensure it is restored again when parsing has
finished.
XPK_ANONSUB
atomic, emits op.
A brace-delimited block of code is expected, and assembled into the body of a new
anonymous subroutine. This will be passed as a protosub CV in the cv field.
XPK_ARITHEXPR
atomic, emits op.
XPK_ARITHEXPR
An arithmetic expression is expected, parsed using "parse_arithexpr()", and passed as an
optree in the op field.
XPK_ARITHEXPR_VOIDCTX, XPK_ARITHEXPR_SCALARCTX
Variants of "XPK_ARITHEXPR" which puts the expression in void or scalar context.
XPK_TERMEXPR
atomic, emits op.
XPK_TERMEXPR
A term expression is expected, parsed using "parse_termexpr()", and passed as an optree in
the op field.
XPK_TERMEXPR_VOIDCTX, XPK_TERMEXPR_SCALARCTX
Variants of "XPK_TERMEXPR" which puts the expression in void or scalar context.
XPK_LISTEXPR
atomic, emits op.
XPK_LISTEXPR
A list expression is expected, parsed using "parse_listexpr()", and passed as an optree in
the op field.
XPK_LISTEXPR_LISTCTX
Variant of "XPK_LISTEXPR" which puts the expression in list context.
XPK_IDENT, XPK_IDENT_OPT
atomic, can probe, emits sv.
A bareword identifier name is expected, and passed as an SV containing a PV in the sv
field. An identifier is not permitted to contain a double colon ("::").
The "_OPT"-suffixed version is optional; if no identifier is found then sv is set to
"NULL".
XPK_PACKAGENAME, XPK_PACKAGENAME_OPT
atomic, can probe, emits sv.
A bareword package name is expected, and passed as an SV containing a PV in the sv field.
A package name is similar to an identifier, except it permits double colons in the middle.
The "_OPT"-suffixed version is optional; if no package name is found then sv is set to
"NULL".
XPK_LEXVARNAME
atomic, emits sv.
XPK_LEXVARNAME(kind)
A lexical variable name is expected, and passed as an SV containing a PV in the sv field.
The "kind" argument specifies what kinds of variable are permitted, and should be a
bitmask of one or more bits from "XPK_LEXVAR_SCALAR", "XPK_LEXVAR_ARRAY" and
"XPK_LEXVAR_HASH". A convenient shortcut "XPK_LEXVAR_ANY" permits all three.
XPK_ATTRIBUTES
atomic, emits i followed by more args.
A list of ":"-prefixed attributes is expected, in the same format as sub or variable
attributes. An optional leading ":" indicates the presence of attributes, then one or more
of them are parsed. Attributes may be optionally separated by additional ":"s, but this is
not required.
Each attribute is expected to be an identifier name, followed by an optional value wrapped
in parentheses. Whitespace is NOT permitted between the name and value, as per standard
Perl parsing rules.
:attrname
:attrname(value)
The i field indicates how many attributes were found. That number of additional arguments
are then passed, each containing two SVs in the attr.name and attr.value fields. This
number may be zero.
It is not an error for there to be no attributes present, or for the optional colon to be
missing. In this case i will be set to zero.
XPK_VSTRING, XPK_VSTRING_OPT
atomic, can probe, emits sv.
A version string is expected, of the form "v1.234" including the leading "v" character. It
is passed as a version SV object in the sv field.
The "_OPT"-suffixed version is optional; if no version string is found then sv is set to
"NULL".
XPK_LEXVAR_MY
atomic, emits padix.
XPK_LEXVAR_MY(kind)
A lexical variable name is expected, added to the current pad as if specified in a "my"
expression, and passed as the pad index in the padix field.
The "kind" argument specifies what kinds of variable are permitted, as per
"XPK_LEXVARNAME".
XPK_COMMA, XPK_COLON, XPK_EQUALS
atomic, can probe, emits nothing.
A literal character (",", ":" or "=") is expected. No argument value is passed.
XPK_AUTOSEMI
atomic, emits nothing.
A literal semicolon (";") as a statement terminator is optionally expected. If the next
token is a closing brace to indicate the end of a block, then a semicolon is not required.
If anything else is encountered an error will be raised.
This piece type is the same as specifying the "XPK_FLAG_AUTOSEMI". It is useful to put at
the end of a sequence that forms part of a choice of syntax, where some forms indicate a
statement ending in a semicolon, whereas others may end in a full block that does not need
one.
XPK_INFIX_*
atomic, can probe, emits infix.
An infix operator as recognised by XS::Parse::Infix. The returned pointer points to a
structure allocated by "XS::Parse::Infix" describing the operator.
Various versions of the macro are provided, each using a different selection filter to
choose certain available infix operators:
XPK_INFIX_RELATION # any relational operator
XPK_INFIX_EQUALITY # an equality operator like `==` or `eq`
XPK_INFIX_MATCH_NOSMART # any sort of "match"-like operator, except smartmatch
XPK_INFIX_MATCH_SMART # XPK_INFIX_MATCH_NOSMART plus smartmatch
XPK_LITERAL
atomic, can probe, emits nothing.
XPK_LITERAL("literal")
A literal string match is expected. No argument value is passed.
This form should generally be avoided if at all possible, because it is very easy to abuse
to make syntaxes which confuse humans and code tools alike. Generally it is best reserved
just for the first component of a "XPK_OPTIONAL" or "XPK_REPEATED" sequence, to provide a
"secondary keyword" that such a repeated item can look out for.
XPK_KEYWORD
atomic, can probe, emits nothing.
XPK_KEYWORD("keyword")
A literal string match is expected. No argument value is passed.
This is similar to "XPK_LITERAL" except that it additionally checks that the following
character is not an identifier character. This ensures that the expected keyword-like
behaviour is preserved. For example, given the input "keyword", the piece
"XPK_LITERAL("key")" would match it, whereas "XPK_KEYWORD("key")" would not because of the
subsequent "w" character.
XPK_SEQUENCE
structural, might support probe, emits nothing.
XPK_SEQUENCE(pieces ...)
A structural type which contains a number of pieces. This is normally equivalent to simply
placing the pieces in sequence inside their own container, but it is useful inside
"XPK_CHOICE" or "XPK_TAGGEDCHOICE".
An "XPK_SEQUENCE" supports probe if its first contained piece does; i.e. is transparent
to probing.
XPK_OPTIONAL
structural, emits i.
XPK_OPTIONAL(pieces ...)
A structural type which may expects to find its contained pieces, or is happy not to. This
will pass an argument whose i field contains either 1 or 0, depending whether the contents
were found. The first piece type within must support probe.
XPK_REPEATED
structural, emits i.
XPK_REPEATED(pieces ...)
A structural type which expects to find zero or more repeats of its contained pieces. This
will pass an argument whose i field contains the count of the number of repeats it found.
The first piece type within must support probe.
XPK_CHOICE
structural, can probe, emits i.
XPK_CHOICE(options ...)
A structural type which expects to find one of a number of alternative options. An ordered
list of types is provided, all of which must support probe. This will pass an argument
whose i field gives the index of the first choice that was accepted. The first option
takes the value 0.
As each of the options is interpreted as an alternative, not a sequence, you should use
"XPK_SEQUENCE" if a sequence of multiple items should be considered as a single
alternative.
It is not an error if no choice matches. At that point, the i field will be set to -1.
If you require a failure message in this case, set the final choice to be of type
"XPK_FAILURE". This will cause an error message to be printed instead.
XPK_FAILURE("message string")
XPK_TAGGEDCHOICE
structural, can probe, emits i.
XPK_TAGGEDCHOICE(choice, tag, ...)
A structural type similar to "XPK_CHOICE", except that each choice type is followed by an
element of type "XPK_TAG" which gives an integer. It is that integer value, rather than
the positional index of the choice within the list, which is passed in the i field.
XPK_TAG(value)
As each of the options is interpreted as an alternative, not a sequence, you should use
"XPK_SEQUENCE" if a sequence of multiple items should be considered as a single
alternative.
XPK_COMMALIST
structural, might support probe, emits i.
XPK_COMMALIST(pieces ...)
A structural type which expects to find one or more repeats of its contained pieces,
separated by literal comma (",") characters. This is somewhat similar to "XPK_REPEATED",
except that it needs at least one copy, needs commas between its items, but does not
require that the first contained piece support probe (the comma itself is sufficient to
indicate a repeat).
An "XPK_COMMALIST" supports probe if its first contained piece does; i.e. is transparent
to probing.
XPK_PARENSCOPE
structural, can probe, emits nothing.
XPK_PARENSCOPE(pieces ...)
A structural type which expects to find a sequence of pieces, all contained in parentheses
as "( ... )". This will pass no extra arguments.
XPK_ARGSCOPE
structural, emits nothing.
XPK_ARGSCOPE(pieces ...)
A structural type similar to "XPK_PARENSCOPE", except that the parentheses themselves are
optional; much like Perl's parsing of calls to known functions.
If parentheses are encountered in the input, they will be consumed by this piece and it
will behave identically to "XPK_PARENSCOPE". If there is no open parenthesis, this piece
will behave like "XPK_SEQUENCE" and consume all the pieces inside it, without expecting a
closing parenthesis.
XPK_BRACKETSCOPE
structural, can probe, emits nothing.
XPK_BRACKETSCOPE(pieces ...)
A structural type which expects to find a sequence of pieces, all contained in square
brackets as "[ ... ]". This will pass no extra arguments.
XPK_BRACESCOPE
structural, can probe, emits nothing.
XPK_BRACESCOPE(pieces ...)
A structural type which expects to find a sequence of pieces, all contained in braces as
"{ ... }". This will pass no extra arguments.
Note that this is not necessary to use with "XPK_BLOCK" or "XPK_ANONSUB"; those will
already consume a set of braces. This is intended for special constrained syntax that
should not just accept an arbitrary block.
XPK_CHEVRONSCOPE
structural, can probe, emits nothing.
XPK_CHEVRONSCOPE(pieces ...)
A structural type which expects to find a sequence of pieces, all contained in angle
brackets as "< ... >". This will pass no extra arguments.
Remember that expressions like "a > b" are valid term expressions, so the contents of this
scope shouldn't allow arbitrary expressions or the closing bracket will be ambiguous.
XPK_PARENSCOPE_OPT, XPK_BRACKETSCOPE_OPT, XPK_BRACESCOPE_OPT, XPK_CHEVRONSCOPE_OPT
structural, can probe, emits i.
XPK_PARENSCOPE_OPT(pieces ...)
XPK_BRACKETSCOPE_OPT(pieces ...)
XPK_BRACESCOPE_OPT(pieces ...)
XPK_CHEVERONSCOPE_OPT(pieces ...)
Each of the four "XPK_...SCOPE" macros above has an optional variant, whose name is
suffixed by "_OPT". These pass an argument whose i field is either true or false,
indicating whether the scope was found, followed by the values from the scope itself.
This is a convenient shortcut to nesting the scope within a "XPK_OPTIONAL" macro.
AUTHOR
Paul Evans <leonerd@leonerd.org.uk>