'\"
'\" Generated from file 'me_ast\&.man' by tcllib/doctools with format 'nroff'
'\" Copyright (c) 2005 Andreas Kupries <andreas_kupries@users\&.sourceforge\&.net>
'\"
.TH "grammar::me_ast" n 0\&.2 tcllib "Grammar operations and usage"
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.BS
.SH NAME
grammar::me_ast \- Various representations of ASTs
.SH DESCRIPTION
This document specifies various representations for the
\fIabstract syntax tree\fRs (short \fIAST\fR) generated by
instances of ME virtual machines, independent of variant\&.
Please go and read the document \fBgrammar::me_intro\fR first if
you do not know what a ME virtual machine is\&.
.PP
ASTs and all the representations we specify distinguish between two
types of nodes, namely:
.PP
.TP
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\&.
.TP
Nonterminal
Nonterminal nodes represent a nonterminal symbol of the grammar used
during parsing\&. They can occur as leaf and inner nodes of the
tree\&.
.PP
.PP
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)\&.
.PP
The root of an AS tree can be either a terminal or nonterminal node\&.
.SH "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\&.
.PP
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\&.
.SH "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
\fBstruct::tree\fR\&. I\&.e it has to support at least all of the
methods described by that package, and may support more\&.
.PP
Because of this the remainder of the specifications is written using
the terms of \fBstruct::tree\fR\&.
.PP
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:
.TP
type
The type of the AST node\&. The recognized values are \fBterminal\fR
and \fBnonterminal\fR\&.
.TP
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\&.
.TP
detail
This attribute is present only for nonterminal nodes\&. It contains the
name of the nonterminal symbol stored in the node\&.
.PP
.SH "EXTENDED AST OBJECTS"
Extended AST objects are like AST objects, with additional
information\&.
.TP
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\&.
.sp
Each element of the list contains the token name, the associated
lexeme attribute, line number, and column index, in this order\&.
.TP
range_lc
This new attribute is defined for all nodes, and contains the
locations from attribute \fIrange\fR translated into line number and
column index\&. Lines are counted from 1, columns are counted from 0\&.
.PP
.SH "BUGS, IDEAS, FEEDBACK"
This document, and the package it describes, will undoubtedly contain
bugs and other problems\&.
Please report such in the category \fIgrammar_me\fR of the
\fITcllib Trackers\fR [http://core\&.tcl\&.tk/tcllib/reportlist]\&.
Please also report any ideas for enhancements you may have for either
package and/or documentation\&.
.PP
When proposing code changes, please provide \fIunified diffs\fR,
i\&.e the output of \fBdiff -u\fR\&.
.PP
Note further that \fIattachments\fR are strongly preferred over
inlined patches\&. Attachments can be made by going to the \fBEdit\fR
form of the ticket immediately after its creation, and then using the
left-most button in the secondary navigation bar\&.
.SH KEYWORDS
AST, abstract syntax tree
.SH CATEGORY
Grammars and finite automata
.SH COPYRIGHT
.nf
Copyright (c) 2005 Andreas Kupries <andreas_kupries@users\&.sourceforge\&.net>

.fi
