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NAME
SYNOPSIS
DESCRIPTION

#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.