pt_parse_peg(3tcl) Parser Tools pt_parse_peg(3tcl)
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NAME
pt_parse_peg - Parser Tools PEG Parser
SYNOPSIS
package require Tcl 8.5
package require pt::parse::peg 1
pt::parse::peg ?objectName?
objectName destroy
objectName parse chan
objectName parset text
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DESCRIPTION
Are you lost ? Do you have trouble understanding this document ? In
that case please read the overview provided by the Introduction to
Parser Tools. This document is the entrypoint to the whole system the
current package is a part of.
This package provides a class whose instances are parsers for parsing
expression grammars in textual form.
CLASS API
pt::parse::peg ?objectName?
The class command constructs parser instances, i.e. objects. The
result of the command is the fully-qualified name of the in-
stance command.
If no objectName is specified the class will generate and use an
automatic name. If the objectName was specified, but is not
fully qualified the command will be created in the current name-
space.
INSTANCES API
All parser instances provide at least the methods shown below:
objectName destroy
This method destroys the parser instance, releasing all claimed
memory and other resources, and deleting the instance command.
The result of the command is the empty string.
objectName parse chan
This method runs the parser using the contents of chan as input
(starting at the current location in the channel), until parsing
is not possible anymore, either because parsing has completed,
or run into a syntax error.
Note here that the Parser Tools are based on Tcl 8.5+. In other
words, the channel argument is not restricted to files, sockets,
etc. We have the full power of reflected channels available.
It should also be noted that the parser pulls the characters
from the input stream as it needs them. If a parser created by
this package has to be operated in a push aka event-driven man-
ner it will be necessary to go to Tcl 8.6+ and use the corou-
tine::auto to wrap it into a coroutine where read is properly
changed for push-operation.
Upon successful completion the command returns an abstract syn-
tax tree as its result. This AST is in the form specified in
section AST serialization format. As a plain nested Tcl-list it
can then be processed with any Tcl commands the user likes, do-
ing transformations, semantic checks, etc. To help in this the
package pt::ast provides a set of convenience commands for vali-
dation of the tree's basic structure, printing it for debugging,
and walking it either from the bottom up, or top down.
When encountering a syntax error the command will throw an error
instead. This error will be a 4-element Tcl-list, containing,
in the order listed below:
[1] The string pt::rde identifying it as parser runtime er-
ror.
[2] The location of the parse error, as character offset from
the beginning of the parsed input.
[3] The location of parse error, now as a 2-element list con-
taining line-number and column in the line.
[4] A set of atomic parsing expressions indicating encoding
the characters and/or nonterminal symbols the parser ex-
pected to see at the location of the parse error, but did
not get. For the specification of atomic parsing expres-
sions please see the section PE serialization format.
objectName parset text
This method runs the parser using the string in text as input.
In all other ways it behaves like the method parse, shown above.
BUGS, IDEAS, FEEDBACK
This document, and the package it describes, will undoubtedly contain
bugs and other problems. Please report such in the category pt 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
EBNF, LL(k), PEG, TDPL, context-free languages, expression, grammar,
matching, parser, parsing expression, parsing expression grammar, push
down automaton, recursive descent, state, top-down parsing languages,
transducer
CATEGORY
Parsing and Grammars
COPYRIGHT
Copyright (c) 2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>
tcllib 1 pt_parse_peg(3tcl)