man Devel::CallParser (3): 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.