NAME

XS::Parse::Sublike - XS functions to assist in parsing sub-like syntax

DESCRIPTION

This module provides some XS functions to assist in writing parsers for sub-like 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_sublike

  void boot_xs_parse_sublike(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_sublike(0.04);

xs_parse_sublike

   int xs_parse_sublike(const struct XSParseSublikeHooks *hooks, void *hookdata, OP **op_ptr)

This function performs the actual parsing of a sub-like keyword. It expects the lexer to be at a position just after the introduction keyword has been consumed, and will proceed to parse an optional name, list of attributes, signature (if enabled by use feature 'signatures'), and code body. The return value and op_ptr can be used directly from the keyword plugin function. It is intended this function be invoked from it, and the result returned directly.

For a more automated handling of keywords, see "register_xs_parse_sublike".

hooks should be a structure that can provide optional function pointers used to customise the parsing process at various stages. hookdata is an opaque pointer which is passed through to each of the hook stage functions.

register_xs_parse_sublike

   void register_xs_parse_sublike(const char *keyword,
     const struct XSParseSublikeHooks *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::Sublike itself.

When the keyword is encountered, the hook's permit function is first tested to see if the keyword is permitted at this point. If the function returns true then the keyword is consumed and parsed as per "xs_parse_sublike".

hookdata is an opaque pointer which is passed through to each of the hook stage functions when they are invoked.

xs_parse_sublike_any

   int xs_parse_sublike_any(const struct XSParseSublikeHooks *hooks, void *hookdata,
     OP **op_ptr)

This function expects to consume an introduction keyword at the lexer position which is either sub or the name of another sub-like keyword, which has been previously registered using "register_xs_parse_sublike". It then proceeds to parse the subsequent syntax similar to how it would have parsed if encountered by the module's own keyword parser plugin, except that the second set of hooks given here also take effect.

If a regular sub is encountered, then this is parsed using the hooks in a similar way to xs_parse_sublike().

If a different registered sub-like keyword is encountered, then parsing is performed using both sets of hooks - the ones given to this function as well as the ones registered with the keyword. This allows their effects to combined. The hooks given by the hooks argument are considered to be on the "outside" from those of the registered keyword "inside". The outside ones run first for all stages, except pre_blockend which runs them inside-out.

hookdata is an opaque pointer which is passed through to each of the hook stage functions when they are invoked.

PARSE CONTEXT

The various hook stages all share state about the ongoing parse process using various fields of the XSParseSublikeContext structure.

   struct XSParseSublikeContext {
      SV *name;
      OP *attrs;
      OP *body;
      CV *cv;
   }

PARSE HOOKS

The XSParseSublikeHooks structure provides the following hook stages, which are invoked in the given order.

The structure has a flags field, which controls various optional parts of operation. The following flags are defined.

XS_PARSE_SUBLIKE_FLAG_FILTERATTRS

If set, the optional filter_attr stage will be invoked.

In addition there are two U8 fields named require_parts and skip_parts which control the behaviour of various parts of the syntax which are usually optional. Any parts with bits set in require_parts become non-optional, and an error if they are missing. Any parts with bits set in skip_parts will skip the relevant part of the parsing process.

When two sets of hooks are combined by the xs_parse_sublike_any function, these bitmasks are accumulated together with inclusive or. Any part required by either set of hooks will still be required; any step skipped by either will be skipped entirely.

If the same bit is set in both fields then the relevant parsing step will not be performed but it will still be an error for that section to be missing. This is likely not useful.

Note that for skipped parts, only the actual parsing steps are skipped. A hook function can still set the relevant fields in the context structure anyway to force a particular value for those parts.

XS_PARSE_SUBLIKE_PART_NAME

The name of the function.

XS_PARSE_SUBLIKE_PART_ATTRS

The attributes of the function.

This part can be skipped, but the bit is ignored when in require_parts. It is always permitted to not provide any additional attributes to a function definition.

XS_PARSE_SUBLIKE_PART_SIGNATURE

The parameter signature of the function.

This part can be skipped, but the bit is ignored when in require_parts. It is always permitted not to provide a signature for a function definition, because such syntax only applies when use feature 'signatures' is in effect, and only on supporting perl versions.

The permit Stage

   bool (*permit)(pTHX_ void *hookdata)

Called by the installed keyword parser hook which is used to handle keywords registered by "register_xs_parse_sublike". This hook stage should inspect whether the keyword is permitted at this time (typically by inspecting the hints hash GvHV(PL_hintgv) for some imported key) and return true only if the keyword is permitted.

Parse Name

At this point, the optional name is parsed and filled into the name field of the context.

The pre_subparse Stage

   void (*pre_subparse)(pTHX_ struct XSParseSublikeContext *ctx, void *hookdata)

Invoked just before start_subparse() is called.

Parse Attrs

At this point the optional sub attributes are parsed and filled into the attrs field of the context, then block_start() is called.

The optional filter_attr Stage

   bool (*filter_attr)(pTHX_ struct XSParseSublikeContext *ctx,
      SV *attr, SV *val, void *hookdata);

If the flags field includes XS_PARSE_SUBLIKE_FLAG_FILTERATTRS then each individual attribute is passed through this optional filter function immediately as each is parsed. attr will be a string SV containing the name of the attribute, and val will either be NULL, or a string SV containing the contents of the parens after its name (without the parens themselves).

If the filter returns true, it indicates that it has in some way handled the attribute and it should not be added to the list given to newATTRSUB(). If the filter returns false it will be handled in the usual way; equivalent to the case where the filter function did not exist.

The post_blockstart Stage

   void (*post_blockstart)(pTHX_ struct XSParseSublikeContext *ctx, void *hookdata)

Invoked after the block_start() function has been called. This hook stage may wish to perform any alterations of PL_compcv or related, inspect or alter the lexical pad, provide hints hash values, or any other tasks before the signature and code body are parsed.

Parse Body

At this point, the main body of the function is parsed and the optree is stored in the body field of the context. If the perl version supports sub signatures and they are enabled and found, the body will be prefixed with the signature ops as well.

The pre_blockend Stage

   void (*pre_blockend)(pTHX_ struct XSParseSublikeContext *ctx, void *hookdata)

Invoked just before the block_end() function is invoked. The hook stage may wish to inspect or alter the optree stored in the body context field.

The post_newcv Stage

   void (*post_newcv)(pTHX_ struct XSParseSublikeContext *ctx, void *hookdata)

Invoked just after newATTRSUB() has been invoked on the optree. The hook stage may wish to inspect or alter the CV stored in the cv context field.

AUTHOR

Paul Evans <leonerd@leonerd.org.uk>