|parrotcode: Parrot abstract syntax tree|
|Contents | Compilers|
PAST - Parrot abstract syntax tree
This file implements the various abstract syntax tree nodes for compiling programs in Parrot.
PAST::Node is the base class for all PAST nodes,
and is derived from PCT::Node.
A node has an array component to hold its children,
and a hash component for its attributes.
we tend to use accessor methods for accessing the node's attributes instead of accessing the hash directly.
Every PAST node inherits
pos attributes from
name attribute is the node's name,
pos are used to identify the location in the original source code for the node.
pos values are generally set by the
node method inherited from
Other node attributes are generally defined by subclasses of
PAST::Val nodes represent constant values in the abstract syntax tree.
name attribute represents the value of the node.
PAST::Var nodes represent variables within the abstract syntax tree.
The variable name (if any) is given as the node's
isdeclattribute (for lexical variables) to
flag. A true value of
isdeclindicates that the variable given by this node is to be created within the current lexical scope. Otherwise, the node refers to a lexical variable from an outer scope.
lvalueattribute, which indicates whether this variable is being used in an lvalue context.
namespace. Useful only for variables with a
slurpyattribute (for parameter variables) to
flag. A true value of
slurpyindicates that the parameter variable given by this node is to be created as a slurpy parameter (consuming all remaining arguments passed in).
typeindicates either the type of the value to create for the node or (future implementation) a PAST tree to create the value.
typeindicates the type of aggregate to create for the base if the base doesn't specify its own 'viviself' attribute.
PAST::Op nodes represent the operations in an abstract syntax tree.
The primary function of the node is given by its
secondary functions may be given by the node's
or other attributes.
pasttypedetermines the type of operation to be performed. Predefined values of
nameattribute, if the node has no
nameattribute then the first child is assumed to evaluate to a callable sub.
inlineattribute (a string). See the
inlinemethod below for details.
nameattribute, then the first child is the invocant and any remaining children are arguments. If the node doesn't have a
nameattribute, then the first child evaluates to the method to be called, the second child is the invocant, and the remaining children are arguments to the method call.
pasttype, then it assumes "pirop" if its
piropattribute is set, otherwise it assumes "call".
pasttypeis "inline". The
codeargument is PIR text to be inserted in the final generated code sequence. Sequences of "%0", "%1", "%2", ... "%9" in
codeare replaced with the evaluated results of the first, second, third, ..., tenth children nodes. (If you need more than ten arguments to your inline PIR, consider making it a subroutine call instead.)
%r - Generate a unique PMC register for the result. %t - Generate a unique PMC register for the result, and initialize it with an object of type C<returns> before the execution of the inline PIR. %u - Re-use the first child's PMC (%0) if it's a temporary result, otherwise same as %t above. %v - (void) Re-use the first child's PMC (%0) as the result of this operation.
PAST::Opattributes based on entries in
hashis an entry in the operator precedence table, and the attributes being set correspond to traits in the grammar.
PAST::Stmts is a container of
PAST::Node without any specific methods.
PAST::Block nodes represent lexical scopes within an abstract syntax tree, and roughly translate to individual Parrot subroutines. A
PAST::Block node nested within another
PAST::Block node acts like a nested lexical scope.
If the block has a
name attribute, that becomes the name of the resulting Parrot sub, otherwise a unique name is automatically generated for the block.
while, and other similar statements).
value. The exception handler can be any PAST tree. The special (string) value "return_pir" generates code to handle
past. The load initializer is a set of operations to be performed as soon as the block is compiled/loaded. For convenience, requests to
loadinitautovivify an empty
PAST::Stmtsnode if one does not already exist.
blockPMC register is automatically initialized to refer to the block itself (to enable attaching properties, adding the block as a method, storing in a symbol table, etc.).
namespaceargument can be either a string or an array of strings.
namein the current block. The HLL is free to select any symbol attributes desired, although the 'scope' attribute is typically used to assist with lexical scoping of PAST::Var nodes.
symbolabove). If no named arguments are given, returns the default attribute hash itself.
nameinstead of the standard PAST compiler.
Patrick Michaud <email@example.com> is the author and maintainer. Please send patches and suggestions to the Parrot porters or Perl 6 compilers mailing lists.
2006-11-20 Patrick Michaud added first draft of POD documentation. 2007-11-21 Re-implementation with pdd26 compliance, compiler toolkit
Copyright (C) 2006-2008, The Perl Foundation.