CONTENTS

• NAME
• SYNOPSIS
• DESCRIPTION
  • Methods
  • Class Hierachy
  • Abstract Syntax Tree structure

#NAME

ExtUtils::ParseXS::Node - Classes for nodes of an Abstract Syntax Tree

#SYNOPSIS

# Create a node to represent the Foo part of an XSUB; then # top-down parse it into a subtree; then top-down emit the # contents of the subtree as C code. my $foo = ExtUtils::ParseXS::Node::Foo->new(); $foo->parse(...) or die; $foo->as_code(...);

#DESCRIPTION

This API is currently private and subject to change.

Node that as of May 2025, this is a Work In Progress. An AST is created for each parsed XSUB, but those nodes aren't yet linked into a higher-level tree representing the whole XS file.

The ExtUtils::ParseXS::Node class, and its various subclasses, hold the state for the nodes of an Abstract Syntax Tree (AST), which represents the parsed state of an XS file.

Each node is a hash of fields. Which field names are legal varies by the node type. The hash keys and values can be accessed directly: there are no getter/setter methods.

Each node may have a kids field which points to an array of all the children of that node: this is what provides the tree structure. In addition, some of those kids may also have direct links from fields for quick access. For example, the xsub_decl child object of an xsub object can be accessed in either of these ways:

$xsub_object->{kids}[0] $xsub_object->{decl}

Most object-valued node fields within a tree point only to their direct children; however, both INPUT_line and OUTPUT_line have an ioparam field which points to the IO_Param object associated with this line, which is located elsewhere in the tree.

The various foo_part nodes divide the parsing of the main body of the XSUB into sections where different sets of keywords are allowable, and where various bits of code can be conveniently emitted.

#Methods

There are two main methods, in addition to new(), which are present in all subclasses. First, parse() consumes lines from the source to satisfy the construct being parsed. It may itself create objects of lower-level constructs and call parse on them. For example, Node::xbody::parse() may create a Node::input_part node and call parse() on it, which will create Node::INPUT or Node::PREINIT nodes as appropriate, and so on.

Secondly, as_code() descends its sub-tree, outputting the tree as C code.

Note that parsing and code-generation are done as two separate phases; parse() should only build a tree and never emit code.

In addition to $self, both these methods are always provided with these three parameters:

#$pxs

An ExtUtils::ParseXS object which contains the overall processing state. In particular, it has warning and croaking methods, and holds the lines read in from the source file for the current paragraph.

#$xsub

The current ExtUtils::ParseXS::xsub node being processed.

#$xbody

The current ExtUtils::ParseXS::xbody node being processed. Note that in the presence of a CASE keyword, an XSUB can have multiple bodies.

The parse() and as_code() methods for some subclasses may have additional parameters.

Some subclasses may have additional helper methods.

#Class Hierachy

Node and its sub-classes form the following inheritance hierarchy. Various abstract classes are used by concrete subclasses where the processing and/or fields are similar: for example, CODE, PPCODE etc all consume a block of uninterpreted lines from the source file until the next keyword, and emit that code, possibly wrapped in #line directives. This common behaviour is provided by the codeblock class.

Node xsub xsub_decl ReturnType Param IO_Param Params xbody input_part init_part code_part output_part cleanup_part autocall oneline NOT_IMPLEMENTED_YET CASE enable EXPORT_XSUB_SYMBOLS PROTOTYPES SCOPE VERSIONCHECK multiline multiline_merged C_ARGS INTERFACE INTERFACE_MACRO OVERLOAD ATTRS PROTOTYPE codeblock CODE CLEANUP INIT POSTCALL PPCODE PREINIT keylines ALIAS INPUT OUTPUT keyline ALIAS_line INPUT_line OUTPUT_line

#Abstract Syntax Tree structure

A typical XSUB might compile to a tree with a structure similar to the following. Note that this is unrelated to the inheritance hierarchy shown above.

xsub xsub_decl ReturnType Params Param Param ... CASE # for when a CASE keyword being present implies multiple # bodies; otherwise, just a bare xbody node. xbody # per-body copy of declaration Params, augmented by # data from INPUT and OUTPUT sections Params IO_Param IO_Param ... input_part INPUT INPUT_line INPUT_line ... PREINIT init_part INIT code_part CODE output_part OUTPUT OUTPUT_line OUTPUT_line ... POSTCALL cleanup_part CLEANUP CASE xbody ...

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