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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  gram-mar::me_intro grammar::me_intro
       mar::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 ele-ments elements
       ments 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 num-ber, number,
              ber, 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://source -
       forge.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)