'\"
'\" Generated from file '/home/aku/Projects/Tcllib/tcllib/embedded/man/files/modules/pt/pt_pgen\&.n' by tcllib/doctools with format 'nroff'
'\" Copyright (c) 2009 Andreas Kupries <andreas_kupries@users\&.sourceforge\&.net>
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'\" The definitions below are for supplemental macros used in Tcl/Tk
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.TH "pt::pgen" n 1\&.0\&.1 tcllib "Parser Tools"
.BS
.SH NAME
pt::pgen \- Parser Generator
.SH SYNOPSIS
package require \fBTcl  8\&.5\fR
.sp
package require \fBpt::pgen  ?1\&.0\&.1?\fR
.sp
\fB::pt::pgen\fR \fIinputformat\fR \fItext\fR \fIresultformat\fR ?\fIoptions\&.\&.\&.\fR?
.sp
.BE
.SH DESCRIPTION
.PP
Are you lost ?
Do you have trouble understanding this document ?
In that case please read the overview provided by the
\fIIntroduction to Parser Tools\fR\&. This document is the
entrypoint to the whole system the current package is a part of\&.
.PP
This package provides a command implementing a
\fIparser generator\fR
taking parsing expression grammars as input\&.
.PP
It is the implementation of method \fBgenerate\fR of \fBpt\fR, the
\fIParser Tools Application\fR\&.
.PP
As such the intended audience of this document are people wishing to
modify and/or extend this part of \fBpt\fR's functionality\&. Users of
\fBpt\fR on the other hand are hereby refered to the applications'
manpage, i\&.e\&. \fIParser Tools Application\fR\&.
.PP
It resides in the User Package Layer of Parser Tools\&.
.PP
IMAGE: arch_user_pkg
.PP
.SH API
.TP
\fB::pt::pgen\fR \fIinputformat\fR \fItext\fR \fIresultformat\fR ?\fIoptions\&.\&.\&.\fR?
This command takes the parsing expression grammar in \fItext\fR (in
the format specified by \fIinputformat\fR), and returns the same
grammar in the format \fIresultformat\fR as the result of the command\&.
.sp
The two known input formats are \fBpeg\fR and \fBjson\fR\&.
Introductions to them, including their formal specifications, can be
found in the \fIPEG Language Tutorial\fR and
\fIThe JSON Grammar Exchange Format\fR\&. The packages used to
parse these formats are
.RS
.TP
\fBpeg\fR
\fBpt::peg::from::peg\fR
.TP
\fBjson\fR
\fBpt::peg::from::json\fR
.RE
.sp
On the output side the known formats, and the packages used to
generate them are
.RS
.TP
\fBc\fR
\fBpt::peg::to::cparam\fR
.TP
\fBcontainer\fR
\fBpt::peg::to::container\fR
.TP
\fBcritcl\fR
\fBpt::peg::to::cparam\fR +
\fBpt::cparam::configuration::critcl\fR
.TP
\fBjson\fR
\fBpt::peg::to::json\fR
.TP
\fBoo\fR
\fBpt::peg::to::tclparam\fR +
\fBpt::tclparam::configuration::tcloo\fR
.TP
\fBpeg\fR
\fBpt::peg::to::peg\fR
.TP
\fBsnit\fR
\fBpt::peg::to::tclparam\fR +
\fBpt::tclparam::configuration::snit\fR
.RE
.IP
The options supported by each of these formats are documented
with their respective packages\&.
.PP
.SH EXAMPLE
In this section we are working a complete example, starting with a PEG
grammar and ending with running the parser generated from it over some
input, following the outline shown in the figure below:
.PP
IMAGE: flow
.PP
Our grammar, assumed to the stored in the file "\fIcalculator\&.peg\fR"
is
.CS


PEG calculator (Expression)
    Digit      <- '0'/'1'/'2'/'3'/'4'/'5'/'6'/'7'/'8'/'9'       ;
    Sign       <- '-' / '+'                                     ;
    Number     <- Sign? Digit+                                  ;
    Expression <- Term (AddOp Term)*                            ;
    MulOp      <- '*' / '/'                                     ;
    Term       <- Factor (MulOp Factor)*                        ;
    AddOp      <- '+'/'-'                                       ;
    Factor     <- '(' Expression ')' / Number                   ;
END;

.CE
From this we create a snit-based parser
using the script "\fIgen\fR"
.CS


package require Tcl 8\&.5
package require fileutil
package require pt::pgen

lassign $argv name
set grammar [fileutil::cat $name\&.peg]
set pclass  [pt::pgen peg $gr snit -class $name -file  $name\&.peg -name  $name]
fileutil::writeFile $name\&.tcl $pclass
exit 0

.CE
calling it like
.CS

 tclsh8\&.5 gen calculator
.CE
which leaves us with the parser package and class written to the file
"\fIcalculator\&.tcl\fR"\&.
Assuming that this package is then properly installed in a place where
Tcl can find it we can now use this class via a script like
.CS


    package require calculator

    lassign $argv input
    set channel [open $input r]

    set parser [calculator]
    set ast [$parser parse $channel]
    $parser destroy
    close $channel

    \&.\&.\&. now process the returned abstract syntax tree \&.\&.\&.

.CE
where the abstract syntax tree stored in the variable will look like
.PP
.CS


set ast {Expression 0 4
    {Factor 0 4
        {Term 0 2
            {Number 0 2
                {Digit 0 0}
                {Digit 1 1}
                {Digit 2 2}
            }
        }
        {AddOp 3 3}
        {Term 4 4
            {Number 4 4
                {Digit 4 4}
            }
        }
    }
}

.CE
.PP
assuming that the input file and channel contained the text
.CS

 120+5
.CE
A more graphical representation of the tree would be
.PP
.PS
\&.nf
+- Digit 0 0 | 1
|            |
+- Term 0 2 --- Number 0 2 -+- Digit 1 1 | 2
|                           |            |
|                           +- Digit 2 2 | 0
|                                        |
Expression 0 4 --- Factor 0 4 -+----------------------------- AddOp 3 3 | +
|                                        |
+- Term 4 4 --- Number 4 4 --- Digit 4 4 | 5
\&.fi
.PE
.PP
Regardless, at this point it is the user's responsibility to work with
the tree to reach whatever goal she desires\&. I\&.e\&. analyze it,
transform it, etc\&. The package \fBpt::ast\fR should be of help
here, providing commands to walk such ASTs structures in various ways\&.
.PP
One important thing to note is that the parsers used here return a
data structure representing the structure of the input per the grammar
underlying the parser\&. There are \fIno\fR callbacks during the
parsing process, i\&.e\&. no \fIparsing actions\fR, as most other
parsers will have\&.
.PP
Going back to the last snippet of code, the execution of the parser
for some input, note how the parser instance follows the specified
\fIParser API\fR\&.
.SH "BUGS, IDEAS, FEEDBACK"
This document, and the package it describes, will undoubtedly contain
bugs and other problems\&.
Please report such in the category \fIpt\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\&.
.SH 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
.SH CATEGORY
Parsing and Grammars
.SH COPYRIGHT
.nf
Copyright (c) 2009 Andreas Kupries <andreas_kupries@users\&.sourceforge\&.net>

.fi