'\"
'\" Generated from file 'pt_from_api\&.man' by tcllib/doctools with format 'nroff'
'\" Copyright (c) 2009 Andreas Kupries <andreas_kupries@users\&.sourceforge\&.net>
'\"
.TH "pt_import_api" i 1 tcllib "Parser Tools"
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.BS
.SH NAME
pt_import_api \- Parser Tools Import API
.SH SYNOPSIS
package require \fBTcl  8\&.5\fR
.sp
\fBCONVERTER\fR \fBconvert\fR \fItext\fR
.sp
\fBIncludeFile\fR \fIcurrentfile\fR \fIpath\fR
.sp
\fB::import\fR \fItext\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 document describes two APIs\&. First the API shared by all packages
for the conversion of some other format into Parsing Expression
Grammars , and then the API shared by the packages which implement the
import plugins sitting on top of the conversion packages\&.
.PP
Its intended audience are people who wish to create their own
converter for some type of input, and/or an import plugin for their or
some other converter\&.
.PP
It resides in the Import section of the Core Layer of Parser Tools\&.
.PP
IMAGE: arch_core_import
.PP
.SH "CONVERTER API"
Any (grammar) import converter has to follow the rules set out below:
.IP [1]
A converter is a package\&. Its name is arbitrary, however it is
recommended to put it under the \fB::pt::peg::from\fR
namespace\&.
.IP [2]
The package provides either a single Tcl command following the
API outlined below, or a class command whose instances follow
the same API\&. The commands which follow the API are called
\fIconverter commands\fR\&.
.IP [3]
A converter command has to provide the following single method
with the given signature and semantic\&. Converter commands
are allowed to provide more methods of their own, but not
less, and they may not provide different semantics for the
standardized method\&.
.RS
.TP
\fBCONVERTER\fR \fBconvert\fR \fItext\fR
This method has to accept some \fItext\fR, a parsing expression
grammar in some format\&.
The result of the method has to be the canonical serialization of a
parsing expression grammar, as specified in section
\fBPEG serialization format\fR, the result of reading and
converting the input text\&.
.RE
.PP
.SH "PLUGIN API"
Any (grammar) import plugin has to follow the rules set out below:
.IP [1]
A plugin is a package\&.
.IP [2]
The name of a plugin package has the form
pt::peg::import::\fBFOO\fR,
where \fBFOO\fR is the name of the format the plugin will
accept input for\&.
.IP [3]
The plugin can expect that the package
\fBpt::peg::import::plugin\fR is present, as
indicator that it was invoked from a genuine plugin manager\&.
.sp
It is recommended that a plugin does check for the presence of
this package\&.
.IP [4]
The plugin can expect that a command named \fBIncludeFile\fR
is present, with the signature
.RS
.TP
\fBIncludeFile\fR \fIcurrentfile\fR \fIpath\fR
This command has to be invoked by the plugin when it has to process an
included file, if the format has the concept of such\&.
.sp
The plugin has to supply the following arguments
.RS
.TP
string \fIcurrentfile\fR
The path of the file it is currently processing\&. This may be the empty
string if no such is known\&.
.TP
string \fIpath\fR
The path of the include file as specified in the include directive
being processed\&.
.RE
.IP
The result of the command will be a 5-element list containing
.RS
.IP [1]
A boolean flag indicating the success (\fBTrue\fR) or failure
(\fBFalse\fR) of the operation\&.
.IP [2]
In case of success the contents of the included file, and the
empty string otherwise\&.
.IP [3]
The resolved, i\&.e\&. absolute path of the included file, if
possible, or the unchanged \fIpath\fR argument\&. This is for
display in an error message, or as the \fIcurrentfile\fR
argument of another call to \fBIncludeFile\fR should this file
contain more files\&.
.IP [4]
In case of success an empty string, and for failure a code
indicating the reason for it, one of
.RS
.TP
notfound
The specified file could not be found\&.
.TP
notread
The specified file was found, but not be read into memory\&.
.RE
.IP [5]
An empty string in case of success of a \fBnotfound\fR
failure, and an additional error message describing the reason
for a \fBnotread\fR error in more detail\&.
.RE
.RE
.IP [5]
A plugin has to provide a single command, in the global
namespace, with the signature shown below\&. Plugins are allowed
to provide more commands of their own, but not less, and they
may not provide different semantics for the standardized
command\&.
.RS
.TP
\fB::import\fR \fItext\fR
This command has to accept the a text containing a parsing expression
grammar in some format\&. The result of the command has to be the result
of the converter invoked by the plugin for the input grammar, the
canonical serialization of the parsing expression grammar contained in
the input\&.
.RS
.TP
string \fItext\fR
This argument will contain the parsing expression grammar for which to
generate the serialization\&.
The specification of what a \fIcanonical\fR serialization is can be
found in the section \fBPEG serialization format\fR\&.
.RE
.RE
.IP [6]
A single usage cycle of a plugin consists of an invokation of
the command \fBimport\fR\&. This call has to leave the plugin in
a state where another usage cycle can be run without problems\&.
.PP
.SH USAGE
To use a converter do
.CS


    # Get the converter (single command here, not class)
    package require the-converter-package

    # Perform the conversion
    set serial [theconverter convert $thegrammartext]

    \&.\&.\&. process the result \&.\&.\&.

.CE
To use a plugin \fBFOO\fR do
.CS


    # Get an import plugin manager
    package require pt::peg::import
    pt::peg::import I

    # Run the plugin, and the converter inside\&.
    set serial [I import serial $thegrammartext FOO]

    \&.\&.\&. process the result \&.\&.\&.

.CE
.SH "PEG SERIALIZATION FORMAT"
Here we specify the format used by the Parser Tools to serialize
Parsing Expression Grammars as immutable values for transport,
comparison, etc\&.
.PP
We distinguish between \fIregular\fR and \fIcanonical\fR
serializations\&.
While a PEG may have more than one regular serialization only exactly
one of them will be \fIcanonical\fR\&.
.TP
regular serialization
.RS
.IP [1]
The serialization of any PEG is a nested Tcl dictionary\&.
.IP [2]
This dictionary holds a single key, \fBpt::grammar::peg\fR, and its
value\&. This value holds the contents of the grammar\&.
.IP [3]
The contents of the grammar are a Tcl dictionary holding the set of
nonterminal symbols and the starting expression\&. The relevant keys and
their values are
.RS
.TP
\fBrules\fR
The value is a Tcl dictionary whose keys are the names of the
nonterminal symbols known to the grammar\&.
.RS
.IP [1]
Each nonterminal symbol may occur only once\&.
.IP [2]
The empty string is not a legal nonterminal symbol\&.
.IP [3]
The value for each symbol is a Tcl dictionary itself\&. The relevant
keys and their values in this dictionary are
.RS
.TP
\fBis\fR
The value is the serialization of the parsing expression describing
the symbols sentennial structure, as specified in the section
\fBPE serialization format\fR\&.
.TP
\fBmode\fR
The value can be one of three values specifying how a parser should
handle the semantic value produced by the symbol\&.
.RS
.TP
\fBvalue\fR
The semantic value of the nonterminal symbol is an abstract syntax
tree consisting of a single node node for the nonterminal itself,
which has the ASTs of the symbol's right hand side as its children\&.
.TP
\fBleaf\fR
The semantic value of the nonterminal symbol is an abstract syntax
tree consisting of a single node node for the nonterminal, without any
children\&. Any ASTs generated by the symbol's right hand side are
discarded\&.
.TP
\fBvoid\fR
The nonterminal has no semantic value\&. Any ASTs generated by the
symbol's right hand side are discarded (as well)\&.
.RE
.RE
.RE
.TP
\fBstart\fR
The value is the serialization of the start parsing expression of the
grammar, as specified in the section \fBPE serialization format\fR\&.
.RE
.IP [4]
The terminal symbols of the grammar are specified implicitly as the
set of all terminal symbols used in the start expression and on the
RHS of the grammar rules\&.
.RE
.TP
canonical serialization
The canonical serialization of a grammar has the format as specified
in the previous item, and then additionally satisfies the constraints
below, which make it unique among all the possible serializations of
this grammar\&.
.RS
.IP [1]
The keys found in all the nested Tcl dictionaries are sorted in
ascending dictionary order, as generated by Tcl's builtin command
\fBlsort -increasing -dict\fR\&.
.IP [2]
The string representation of the value is the canonical representation
of a Tcl dictionary\&. I\&.e\&. it does not contain superfluous whitespace\&.
.RE
.PP
.SS EXAMPLE
Assuming the following PEG for simple mathematical expressions
.PP
.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
.PP
then its canonical serialization (except for whitespace) is
.PP
.CS


pt::grammar::peg {
    rules {
        AddOp      {is {/ {t -} {t +}}                                                                mode value}
        Digit      {is {/ {t 0} {t 1} {t 2} {t 3} {t 4} {t 5} {t 6} {t 7} {t 8} {t 9}}                mode value}
        Expression {is {x {n Term} {* {x {n AddOp} {n Term}}}}                                        mode value}
        Factor     {is {/ {x {t (} {n Expression} {t )}} {n Number}}                                  mode value}
        MulOp      {is {/ {t *} {t /}}                                                                mode value}
        Number     {is {x {? {n Sign}} {+ {n Digit}}}                                                 mode value}
        Sign       {is {/ {t -} {t +}}                                                                mode value}
        Term       {is {x {n Factor} {* {x {n MulOp} {n Factor}}}}                                    mode value}
    }
    start {n Expression}
}

.CE
.PP
.SH "PE SERIALIZATION FORMAT"
Here we specify the format used by the Parser Tools to serialize
Parsing Expressions as immutable values for transport, comparison,
etc\&.
.PP
We distinguish between \fIregular\fR and \fIcanonical\fR
serializations\&.
While a parsing expression may have more than one regular
serialization only exactly one of them will be \fIcanonical\fR\&.
.TP
Regular serialization
.RS
.TP
\fBAtomic Parsing Expressions\fR
.RS
.IP [1]
The string \fBepsilon\fR is an atomic parsing expression\&. It matches
the empty string\&.
.IP [2]
The string \fBdot\fR is an atomic parsing expression\&. It matches
any character\&.
.IP [3]
The string \fBalnum\fR is an atomic parsing expression\&. It matches
any Unicode alphabet or digit character\&. This is a custom extension of
PEs based on Tcl's builtin command \fBstring is\fR\&.
.IP [4]
The string \fBalpha\fR is an atomic parsing expression\&. It matches
any Unicode alphabet character\&. This is a custom extension of PEs
based on Tcl's builtin command \fBstring is\fR\&.
.IP [5]
The string \fBascii\fR is an atomic parsing expression\&. It matches
any Unicode character below U0080\&. This is a custom extension of PEs
based on Tcl's builtin command \fBstring is\fR\&.
.IP [6]
The string \fBcontrol\fR is an atomic parsing expression\&. It matches
any Unicode control character\&. This is a custom extension of PEs based
on Tcl's builtin command \fBstring is\fR\&.
.IP [7]
The string \fBdigit\fR is an atomic parsing expression\&. It matches
any Unicode digit character\&. Note that this includes characters
outside of the [0\&.\&.9] range\&. This is a custom extension of PEs
based on Tcl's builtin command \fBstring is\fR\&.
.IP [8]
The string \fBgraph\fR is an atomic parsing expression\&. It matches
any Unicode printing character, except for space\&. This is a custom
extension of PEs based on Tcl's builtin command \fBstring is\fR\&.
.IP [9]
The string \fBlower\fR is an atomic parsing expression\&. It matches
any Unicode lower-case alphabet character\&. This is a custom extension
of PEs based on Tcl's builtin command \fBstring is\fR\&.
.IP [10]
The string \fBprint\fR is an atomic parsing expression\&. It matches
any Unicode printing character, including space\&. This is a custom
extension of PEs based on Tcl's builtin command \fBstring is\fR\&.
.IP [11]
The string \fBpunct\fR is an atomic parsing expression\&. It matches
any Unicode punctuation character\&. This is a custom extension of PEs
based on Tcl's builtin command \fBstring is\fR\&.
.IP [12]
The string \fBspace\fR is an atomic parsing expression\&. It matches
any Unicode space character\&. This is a custom extension of PEs based
on Tcl's builtin command \fBstring is\fR\&.
.IP [13]
The string \fBupper\fR is an atomic parsing expression\&. It matches
any Unicode upper-case alphabet character\&. This is a custom extension
of PEs based on Tcl's builtin command \fBstring is\fR\&.
.IP [14]
The string \fBwordchar\fR is an atomic parsing expression\&. It
matches any Unicode word character\&. This is any alphanumeric character
(see alnum), and any connector punctuation characters (e\&.g\&.
underscore)\&. This is a custom extension of PEs based on Tcl's builtin
command \fBstring is\fR\&.
.IP [15]
The string \fBxdigit\fR is an atomic parsing expression\&. It matches
any hexadecimal digit character\&. This is a custom extension of PEs
based on Tcl's builtin command \fBstring is\fR\&.
.IP [16]
The string \fBddigit\fR is an atomic parsing expression\&. It matches
any decimal digit character\&. This is a custom extension of PEs based
on Tcl's builtin command \fBregexp\fR\&.
.IP [17]
The expression
[list t \fBx\fR]
is an atomic parsing expression\&. It matches the terminal string \fBx\fR\&.
.IP [18]
The expression
[list n \fBA\fR]
is an atomic parsing expression\&. It matches the nonterminal \fBA\fR\&.
.RE
.TP
\fBCombined Parsing Expressions\fR
.RS
.IP [1]
For parsing expressions \fBe1\fR, \fBe2\fR, \&.\&.\&. the result of
[list / \fBe1\fR \fBe2\fR \&.\&.\&. ]
is a parsing expression as well\&.
This is the \fIordered choice\fR, aka \fIprioritized choice\fR\&.
.IP [2]
For parsing expressions \fBe1\fR, \fBe2\fR, \&.\&.\&. the result of
[list x \fBe1\fR \fBe2\fR \&.\&.\&. ]
is a parsing expression as well\&.
This is the \fIsequence\fR\&.
.IP [3]
For a parsing expression \fBe\fR the result of
[list * \fBe\fR]
is a parsing expression as well\&.
This is the \fIkleene closure\fR, describing zero or more
repetitions\&.
.IP [4]
For a parsing expression \fBe\fR the result of
[list + \fBe\fR]
is a parsing expression as well\&.
This is the \fIpositive kleene closure\fR, describing one or more
repetitions\&.
.IP [5]
For a parsing expression \fBe\fR the result of
[list & \fBe\fR]
is a parsing expression as well\&.
This is the \fIand lookahead predicate\fR\&.
.IP [6]
For a parsing expression \fBe\fR the result of
[list ! \fBe\fR]
is a parsing expression as well\&.
This is the \fInot lookahead predicate\fR\&.
.IP [7]
For a parsing expression \fBe\fR the result of
[list ? \fBe\fR]
is a parsing expression as well\&.
This is the \fIoptional input\fR\&.
.RE
.RE
.TP
Canonical serialization
The canonical serialization of a parsing expression has the format as
specified in the previous item, and then additionally satisfies the
constraints below, which make it unique among all the possible
serializations of this parsing expression\&.
.RS
.IP [1]
The string representation of the value is the canonical representation
of a pure Tcl list\&. I\&.e\&. it does not contain superfluous whitespace\&.
.IP [2]
Terminals are \fInot\fR encoded as ranges (where start and end of the
range are identical)\&.
.RE
.PP
.PP
.SS EXAMPLE
Assuming the parsing expression shown on the right-hand side of the
rule
.PP
.CS


    Expression <- Term (AddOp Term)*

.CE
.PP
then its canonical serialization (except for whitespace) is
.PP
.CS


    {x {n Term} {* {x {n AddOp} {n Term}}}}

.CE
.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 \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\&.
.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
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