grammar::me_ast(3tcl) Grammar operations and usage grammar::me_ast(3tcl)
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NAME
grammar::me_ast - Various representations of ASTs
DESCRIPTION
This document specifies various representations for the abstract syntax
trees (short AST) generated by instances of ME virtual machines, inde-
pendent of variant. Please go and read the document grammar::me_intro
first if you do not know what a ME virtual machine is.
ASTs and all the representations we specify distinguish between two
types of nodes, namely:
Terminal
Terminal nodes refer to the terminal symbols found in the token
stream. They are always leaf nodes. I.e. terminal nodes never
have children.
Nonterminal
Nonterminal nodes represent a nonterminal symbol of the grammar
used during parsing. They can occur as leaf and inner nodes of
the tree.
Both types of nodes carry basic range information telling a user which
parts of the input are covered by the node by providing the location of
the first and last tokens found within the range. Locations are pro-
vided as non-negative integer offsets from the beginning of the token
stream, with the first token found in the stream located at offset 0
(zero).
The root of an AS tree can be either a terminal or nonterminal node.
AST VALUES
This representation of ASTs is a Tcl list. The main list represents the
root node of the tree, with the representations of the children nested
within.
Each node is represented by a single Tcl list containing three or more
elements. The first element is either the empty string or the name of a
nonterminal symbol (which is never the empty string). The second and
third elements are then the locations of the first and last tokens.
Any additional elements after the third are then the representations of
the children, with the leftmost child first, i.e. as the fourth element
of the list representing the node.
AST OBJECTS
In this representation an AST is represented by a Tcl object command
whose API is compatible to the tree objects provided by the package
struct::tree. I.e it has to support at least all of the methods de-
scribed by that package, and may support more.
Because of this the remainder of the specifications is written using
the terms of struct::tree.
Each node of the AST directly maps to a node in the tree object. All
data beyond the child nodes, i.e. node type and input locations, are
stored in attributes of the node in the tree object. They are:
type The type of the AST node. The recognized values are terminal and
nonterminal.
range The locations of the first and last token of the terminal data
in the input covered by the node. This is a list containing two
locations.
detail This attribute is present only for nonterminal nodes. It con-
tains the name of the nonterminal symbol stored in the node.
EXTENDED AST OBJECTS
Extended AST objects are like AST objects, with additional information.
detail This attribute is now present at all nodes. Its contents are un-
changed for nonterminal nodes. For terminal nodes it contains a
list describing all tokens from the input which are covered by
the node.
Each element of the list contains the token name, the associated
lexeme attribute, line number, and column index, in this order.
range_lc
This new attribute is defined for all nodes, and contains the
locations from attribute range translated into line number and
column index. Lines are counted from 1, columns are counted from
0.
BUGS, IDEAS, FEEDBACK
This document, and the package it describes, will undoubtedly contain
bugs and other problems. Please report such in the category grammar_me
of the Tcllib Trackers [http://core.tcl.tk/tcllib/reportlist]. Please
also report any ideas for enhancements you may have for either package
and/or documentation.
When proposing code changes, please provide unified diffs, i.e the out-
put of diff -u.
Note further that attachments are strongly preferred over inlined
patches. Attachments can be made by going to the Edit form of the
ticket immediately after its creation, and then using the left-most
button in the secondary navigation bar.
KEYWORDS
AST, abstract syntax tree
CATEGORY
Grammars and finite automata
COPYRIGHT
Copyright (c) 2005 Andreas Kupries <andreas_kupries@users.sourceforge.net>
tcllib 0.1 grammar::me_ast(3tcl)