Devel::CallParser(3)

NAME
Devel::CallParser - custom parsing attached to subroutines

SYNOPSIS
        # to generate header prior to XS compilation

        perl -MDevel::CallParser=callparser0_h \
                -e 'print callparser0_h' > callparser0.h
        perl -MDevel::CallParser=callparser1_h \
                -e 'print callparser1_h' > callparser1.h

        # in Perl part of module

        use Devel::CallParser;

        /* in XS */

        #include "callparser0.h"

        cv_get_call_parser(cv, &psfun, &psobj);
        static OP *my_psfun(pTHX_ GV *namegv, SV *psobj, U32 *flagsp);
        cv_set_call_parser(cv, my_psfun, psobj);

        #include "callparser1.h"

        cv_get_call_parser(cv, &psfun, &psobj);
        static OP *my_psfun(pTHX_ GV *namegv, SV *psobj, U32 *flagsp);
        cv_set_call_parser(cv, my_psfun, psobj);

        args = parse_args_parenthesised(&flags);
        args = parse_args_nullary(&flags);
        args = parse_args_unary(&flags);
        args = parse_args_list(&flags);
        args = parse_args_block_list(&flags);
        args = parse_args_proto(namegv, protosv, &flags);
        args = parse_args_proto_or_list(namegv, protosv, &flags);

DESCRIPTION
This module provides a C API, for XS modules, concerned with custom parsing. It is centred around the function "cv_set_call_parser", which allows XS code to attach a magical annotation to a Perl subroutine, resulting in resolvable calls to that subroutine having their arguments parsed by arbitrary C code. (This is a more conveniently structured facility than the core's "PL_keyword_plugin" API.) This module makes "cv_set_call_parser" and several supporting functions available.

This module provides the implementation of the functions at runtime. It also, at compile time, supplies the C header file and link library which provide access to the functions. In normal use, "callparser0_h"/"callparser1_h" and "callparser_linkable" should be called at build time (not authoring time) for the module that wishes to use the C functions.

CONSTANTS

callparser0_h
    Content of a C header file, intended to be named ""callparser0.h"". It is to be included in XS code, and "perl.h" must be included first. When the XS module is loaded at runtime, the "Devel::CallParser" module must be loaded first. This will result in a limited form of the C functions "cv_get_call_parser" and "cv_set_call_parser" being available to the XS code.

    The "cv_get_call_parser" and "cv_set_call_parser" functions supplied by this header are mostly as described below. However, for subroutines that have default argument parsing behaviour, "cv_get_call_parser" will return null pointers for the parsing function and its SV argument, rather than pointing to a real function that implements default parsing. Correspondingly, "cv_set_call_parser" will accept such a pair of null pointers to restore default argument parsing for a subroutine. The advantage of these modified semantics is that this much of the functionality is available on Perl versions where it is not possible to implement standard argument parsing as a distinct function. This is the case on all Perl versions prior to 5.13.8.

    This header is only available on Perl versions 5.11.2 and higher.

callparser1_h
    Content of a C header file, intended to be named ""callparser1.h"". It is to be included in XS code, and "perl.h" must be included first. When the XS module is loaded at runtime, the "Devel::CallParser" module must be loaded first. This will result in the C functions "cv_get_call_parser", "cv_set_call_parser", "parse_args_parenthesised", "parse_args_nullary", "parse_args_unary", "parse_args_list", "parse_args_block_list", "parse_args_proto", and "parse_args_proto_or_list", as defined below, being available to the XS code.

    This header is only available on Perl versions 5.13.8 and higher.

callparser_linkable
    List of names of files that must be used as additional objects when linking an XS module that uses the C functions supplied by this module. This list will be empty on many platforms.

C FUNCTIONS

cv_get_call_parser
    Retrieves the function that will be used to parse the arguments for a call to cv. Specifically, the function is used for a subroutine call, not marked with "&", where the callee can be identified at compile time as cv.

    The C-level function pointer is returned in *psfun_p, and an SV argument for it is returned in *psobj_p. The function is intended to be called in this manner:

        argsop = (*psfun_p)(aTHX_ namegv, (*psobj_p), &flags);

    This call is to be made when the parser has just scanned and accepted a bareword and determined that it begins the syntax of a call to cv. namegv is a GV supplying the name that should be used by the parsing function to refer to the callee if it needs to emit any diagnostics, and flags is a "U32" that the parsing function can write to as an additional output. It is permitted to apply the parsing function in non-standard situations, such as to a call to a different subroutine.

    The parsing function's main output is an op tree describing a list of argument expressions. This may be null for an empty list. The argument expressions will be combined with the expression that identified cv and used to build an "entersub" op describing a complete subroutine call. The parsing function may also set flag bits in flags for special effects. The bit "CALLPARSER_PARENS" indicates that the argument list was fully parenthesised, which makes a difference only in obscure situations. The bit "CALLPARSER_STATEMENT" indicates that what was parsed was syntactically not an expression but a statement.

    By default, the parsing function is Perl_parse_args_proto_or_list, and the SV parameter is cv itself. This implements standard subroutine argument parsing. It can be changed, for a particular subroutine, by "cv_set_call_parser".

            void cv_get_call_parser(CV *cv, Perl_call_parser *psfun_p,
                    SV **psobj_p)

cv_set_call_parser
    Sets the function that will be used to parse the arguments for a call to cv. Specifically, the function is used for a subroutine call, not marked with "&", where the callee can be identified at compile time as cv.

    The C-level function pointer is supplied in psfun, and an SV argument for it is supplied in psobj. The function is intended to be called in this manner:

        argsop = (*psfun_p)(aTHX_ namegv, (*psobj_p), &flags);

    This call is to be made when the parser has just scanned and accepted a bareword and determined that it begins the syntax of a call to cv. namegv is a GV supplying the name that should be used by the parsing function to refer to the callee if it needs to emit any diagnostics, and flags is a "U32" that the parsing function can write to as an additional output. It is permitted to apply the parsing function in non-standard situations, such as to a call to a different subroutine.

    The parsing function's main output is an op tree describing a list of argument expressions. This may be null for an empty list. The argument expressions will be combined with the expression that identified cv and used to build an "entersub" op describing a complete subroutine call. The parsing function may also set flag bits in flags for special effects. The bit "CALLPARSER_PARENS" indicates that the argument list was fully parenthesised, which makes a difference only in obscure situations. The bit "CALLPARSER_STATEMENT" indicates that what was parsed was syntactically not an expression but a statement.

    The current setting for a particular CV can be retrieved by "cv_get_call_parser".

            void cv_set_call_parser(CV *cv, Perl_call_parser psfun,
                    SV *psobj)

parse_args_parenthesised
    Parse a parenthesised argument list for a subroutine call. The argument list consists of an optional expression enclosed in parentheses. This is the syntax that is used for any subroutine call where the first thing following the subroutine name is an open parenthesis. It is used regardless of the subroutine's prototype.

    The op tree representing the argument list is returned. The bit "CALLPARSER_PARENS" is set in *flags_p, to indicate that the argument list was fully parenthesised.

            OP *parse_args_parenthesised(U32 *flags_p)

parse_args_nullary
    Parse an argument list for a call to a subroutine that is syntactically a nullary function. The argument list is either parenthesised or completely absent. This is the syntax that is used for a call to a subroutine with a "()" prototype.

    The op tree representing the argument list is returned. The bit "CALLPARSER_PARENS" is set in *flags_p if the argument list was parenthesised.

            OP *parse_args_nullary(U32 *flags_p)

parse_args_unary
    Parse an argument list for a call to a subroutine that is syntactically a unary function. The argument list is either parenthesised, absent, or consists of an unparenthesised arithmetic expression. This is the syntax that is used for a call to a subroutine with prototype "($)", "(;$)", or certain similar prototypes.

    The op tree representing the argument list is returned. The bit "CALLPARSER_PARENS" is set in *flags_p if the argument list was parenthesised.

            OP *parse_args_unary(U32 *flags_p)

parse_args_list
    Parse an argument list for a call to a subroutine that is syntactically a list function. The argument list is either parenthesised, absent, or consists of an unparenthesised list expression. This is the syntax that is used for a call to a subroutine with any prototype that does not have special handling (such as "(@)" or "($$)") or with no prototype at all.

    The op tree representing the argument list is returned. The bit "CALLPARSER_PARENS" is set in *flags_p if the argument list was parenthesised.

            OP *parse_args_list(U32 *flags_p)

parse_args_block_list
    Parse an argument list for a call to a subroutine that is syntactically a block-and-list function. The argument list is either parenthesised, absent, an unparenthesised list expression, or consists of a code block followed by an optionl list expression. Where the first thing seen is an open brace, it is always interpreted as a code block. This is the syntax that is used for a call to a subroutine with any prototype beginning with "&", such as "(&@)" or "(&$)".

    The op tree representing the argument list is returned. The bit "CALLPARSER_PARENS" is set in *flags_p if the argument list was parenthesised.

            OP *parse_args_block_list(U32 *flags_p)

parse_args_proto
    Parse a subroutine argument list based on a subroutine prototype. The syntax used for the argument list will be that implemented by "parse_args_nullary", "parse_args_unary", "parse_args_list", or "parse_args_block_list", depending on the prototype. This is the standard treatment used on a subroutine call, not marked with "&", where the callee can be identified at compile time and has a prototype.

    protosv supplies the subroutine prototype to be applied to the call. It may be a normal defined scalar, of which the string value will be used. Alternatively, for convenience, it may be a subroutine object (a "CV*" that has been cast to "SV*") which has a prototype.

    The namegv parameter would be used to refer to the callee if required in any error message, but currently no message does so.

    The op tree representing the argument list is returned. The bit "CALLPARSER_PARENS" is set in *flags_p if the argument list was parenthesised.

            OP *parse_args_proto(GV *namegv, SV *protosv, U32 *flags_p)

parse_args_proto_or_list
    Parse a subroutine argument list either based on a subroutine prototype or using default list-function syntax. The syntax used for the argument list will be that implemented by "parse_args_nullary", "parse_args_unary", "parse_args_list", or "parse_args_block_list", depending on the prototype. This is the standard treatment used on a subroutine call, not marked with "&", where the callee can be identified at compile time.

    protosv supplies the subroutine prototype to be applied to the call, or indicates that there is no prototype. It may be a normal scalar, in which case if it is defined then the string value will be used as a prototype, and if it is undefined then there is no prototype. Alternatively, for convenience, it may be a subroutine object (a "CV*" that has been cast to "SV*"), of which the prototype will be used if it has one.

    The namegv parameter would be used to refer to the callee if required in any error message, but currently no message does so.

    The op tree representing the argument list is returned. The bit "CALLPARSER_PARENS" is set in *flags_p if the argument list was parenthesised.

            OP *parse_args_proto_or_list(GV *namegv, SV *protosv,
                    U32 *flags_p)

BUGS
Due to reliance on Perl core features to do anything interesting, only a very limited form of custom parsing is possible prior to Perl 5.13.8, and none at all prior to Perl 5.11.2.

The way this module determines which parsing code to use for a subroutine conflicts with the expectations of some particularly tricky modules that use nasty hacks to perform custom parsing without proper support from the Perl core. In particular, this module is incompatible with versions of Devel::Declare prior to 0.006004 and versions of Data::Alias prior to 1.13. An arrangement has been reached that allows later versions of those modules to coexist with this module.

Custom parsing code is only invoked if the subroutine to which it is attached is invoked using an unqualified name. For example, the name "foo" works, but the name "main::foo" will not, despite referring to the same subroutine. This is an unavoidable limitation imposed by the core's interim facility for custom parser plugins. This should be resolved if the API provided by this module, or something similar, migrates into the core in a future version of Perl.

SEE ALSO
Devel::CallChecker

AUTHOR
Andrew Main (Zefram) <zefram@fysh.org>

COPYRIGHT
Copyright (C) 2011, 2013 Andrew Main (Zefram) <zefram@fysh.org>

LICENSE
This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.