


grammar::me_ast(n) Grammar operations and usagegrammar::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,  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
       described by that package, and may support more.




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


       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
              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://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>






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