grammar::me_ast(n)       Grammar operations and usage       grammar::me_ast(n)



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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,
       independent 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
       provided 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
       described 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
              contains 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
              unchanged 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 SF Trackers
       [http://sourceforge.net/tracker/?group_id=12883].  Please also report
       any ideas for enhancements you may have for either package and/or
       documentation.

KEYWORDS
       AST, abstract syntax tree

CATEGORY
       Grammars and finite automata

COPYRIGHT
       Copyright (c) 2005 Andreas Kupries <andreas_kupries@users.sourceforge.net>




grammar_me                            0.1                   grammar::me_ast(n)
