NAME

    XS::Parse::Keyword::FromPerl - drive XS::Parse::Keyword directly from
    Perl

DESCRIPTION

    This module provides a Perl-visible API wrapping (some of) the
    functionality provided by XS::Parse::Keyword, allowing extension
    keywords to be added to the Perl language by writing code in Perl
    itself.

    It provides a thin wrapping later over the XS functions provided by XPK
    itself, and additionally provides some extra perl-visible functions for
    things like optree management, which would normally be written directly
    in C code. No real attempt is made here to provide further abstractions
    on top of the API already provided by Perl and XPK, so users will have
    to be familiar with the overall concepts there as well.

    This module is currently experimental, on top of the
    already-experimental nature of XS::Parse::Keyword itself.

UTILITY FUNCTIONS

    The following helper functions are provided to allow Perl code to get
    access to various parts of the C-level API that would be useful when
    building optrees for keywords. They are not part of the
    XS::Parse::Keyword API.

 opcode

       $type = opcode( $opname );

    Returns an opcode integer corresponding to the given op name, which
    should be lowercase and without the leading OP_... prefix. As this
    involves a linear search across the entire PL_op_name array you may
    wish to perform this just once and store the result, perhaps using use
    constant for convenience.

       use constant OP_CONST => opcode("const");

 new*OP

    This family of functions return a new OP of the given class, for the
    type, flags, and other arguments specified.

    A suitable $type can be obtained by using the "opcode" function.

    $flags contains the opflags; a bitmask of the following constants.

       OPf_WANT OPf_WANT_VOID OPf_WANT_SCALAR OPf_WANT_LIST
       OPf_KIDS
       OPf_PARENS
       OPf_REF
       OPf_MOD
       OPf_STACKED
       OPf_SPECIAL

    The op is returned as a B::OP instance or a subclass thereof.

    These functions can only be called during the build phase of a keyword
    hook, because they depend on having the correct context set by the
    currently-compiling function.

  newOP

       $op = newOP( $type, $flags );

    Returns a new base OP for the given type and flags.

  newUNOP

       $op = newUNOP( $type, $flags, $first );

    Returns a new UNOP for the given type, flags, and first OP child.

  newBINOP

       $op = newBINOP( $type, $flags, $first, $last );

    Returns a new BINOP for the given type, flags, and first and last OP
    child.

  newSVOP

       $op = newSVOP( $type, $flags, $sv );

    Returns a new SVOP for the given type, flags, and SV. A copy of the
    given scalar will be stored in the SVOP itself.

  newGVOP

       $op = newGVOP( $type, $flags, $gvref );

    Returns a new SVOP for the given type, flags, and GV given by a GLOB
    reference. The referred-to GLOB will be stored in the SVOP itself.

XPK FUNCTIONS

 register_xs_parse_keyword

       register_xs_parse_keyword "name" => %args;

    Registers a new extension keyword into the XS::Parse::Keyword registry,
    defined using the given name and arguments.

    Takes the following named arguments:

    flags => INT

      Optional. If present, a bitmask of the following flag constants:

      XPK_FLAG_EXPR

	The build phase is expected to return KEYWORD_PLUGIN_EXPR.

      XPK_FLAG_STMT

	The build phase is expected to return KEYWORD_PLUGIN_STMT.

      XPK_FLAG_AUTOSEMI

	The syntax forms a complete statement, which should be followed by
	;.

    pieces => ARRAY

      Optional. If present, contains definitions for the syntax pieces to
      be parsed for the syntax of this keyword. At present this is not
      supported, so it must be empty.

    permit_hintkey => STRING

      Optional. A string value to use for the "permit_hintkey".

    permit => CODE

      Optional. Callback function for the "permit" phase of keyword
      parsing.

         $ok = $permit->( $hookdata );

      When invoked, it is passed a single arugment containing the
      (optional) hookdata value, and its result should be a boolean scalar.

      At least one of permit_hintkey or permit must be provided.

    check => CODE

      Optional. Callback function for the "check" phase of keyword parsing.

         $check->( $hookdata );

      When invoked, it is passsed a single argument containing the
      (optional) bookdata value.

    build => CODE

      Callback function for the "build" phase of keyword parsing.

         $ret = $build->( \$out, \@args, $hookdata );

      When invoked, it is passed a SCALAR ref to store the output optree
      into, an ARRAY reference containing the parsed arguments, and the
      (optional) hookdata value.

      At present, argument pieces are not supported, so the @args array
      will always be empty.

      The callback function should be build an optree as a B::OP fragment,
      possibly by calling the various new*OP() functions defined above, and
      store the eventual result into the scalar referred to by the first
      argument.

      The callback should return one of KEYWORD_PLUGIN_EXPR or
      KEYWORD_PLUGIN_STMT to indicate how its syntax should be interpreted
      by the perl parser.

    hookdata => SCALAR

      Optional. If present, this scalar value is stored by the keyword
      definition and passed into each of the phase callbacks when invoked.
      If not present then undef will be passed to the callbacks instead.

TODO

      * pieces for parsing.

      * More new*OP() wrapper functions. Support LISTOPs - possibly by just
      passing a list of child ops and doing the OP_LIST + op_convert_list
      dance so users don't have to.

      * More optree-mangling functions. At least, some way to set the TARG
      might be handy; or else some wrappers like hax/newPADxVOP.

AUTHOR

    Paul Evans <leonerd@leonerd.org.uk>