SYNOPSISpackage require Tcl 8.5
package require pt::parse::peg 1
objectName parse chan
objectName parset text
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.
- 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 instance
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 namespace.
INSTANCES APIAll 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 manner it will be necessary to go to Tcl 8.6+ and use the coroutine::auto to wrap it into a coroutine where read is properly changed for push-operation.
Upon successful completion the command returns an abstract syntax 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, doing transformations, semantic checks, etc. To help in this the package pt::ast provides a set of convenience commands for validation 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:
- The string pt::rde identifying it as parser runtime error.
- The location of the parse error, as character offset from the beginning of the parsed input.
- The location of parse error, now as a 2-element list containing line-number and column in the line.
- A set of atomic parsing expressions indicating encoding the characters and/or nonterminal symbols the parser expected to see at the location of the parse error, but did not get. For the specification of atomic parsing expressions 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, FEEDBACKThis 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.
KEYWORDSEBNF, 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
CATEGORYParsing and Grammars
Copyright (c) 2009 Andreas Kupries <[email protected]>