Provided by: tcllib_1.19-dfsg-2_all 
NAME
pt_import_api - Parser Tools Import API
SYNOPSIS
package require Tcl 8.5
CONVERTER convert text
IncludeFile currentfile path
::import text
_________________________________________________________________________________________________
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 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.
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.
It resides in the Import section of the Core Layer of Parser Tools.
IMAGE: arch_core_import
CONVERTER API
Any (grammar) import converter has to follow the rules set out below:
[1] A converter is a package. Its name is arbitrary, however it is recommended to put
it under the ::pt::peg::from namespace.
[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 converter commands.
[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.
CONVERTER convert text
This method has to accept some text, 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 PEG serialization
format, the result of reading and converting the input text.
PLUGIN API
Any (grammar) import plugin has to follow the rules set out below:
[1] A plugin is a package.
[2] The name of a plugin package has the form pt::peg::import::FOO, where FOO is the
name of the format the plugin will accept input for.
[3] The plugin can expect that the package pt::peg::import::plugin is present, as
indicator that it was invoked from a genuine plugin manager.
It is recommended that a plugin does check for the presence of this package.
[4] The plugin can expect that a command named IncludeFile is present, with the
signature
IncludeFile currentfile path
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.
The plugin has to supply the following arguments
string currentfile
The path of the file it is currently processing. This may be the
empty string if no such is known.
string path
The path of the include file as specified in the include directive
being processed.
The result of the command will be a 5-element list containing
[1] A boolean flag indicating the success (True) or failure (False) of
the operation.
[2] In case of success the contents of the included file, and the empty
string otherwise.
[3] The resolved, i.e. absolute path of the included file, if possible,
or the unchanged path argument. This is for display in an error
message, or as the currentfile argument of another call to
IncludeFile should this file contain more files.
[4] In case of success an empty string, and for failure a code indicating
the reason for it, one of
notfound
The specified file could not be found.
notread
The specified file was found, but not be read into memory.
[5] An empty string in case of success of a notfound failure, and an
additional error message describing the reason for a notread error in
more detail.
[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.
::import text
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.
string text
This argument will contain the parsing expression grammar for which
to generate the serialization. The specification of what a canonical
serialization is can be found in the section PEG serialization
format.
[6] A single usage cycle of a plugin consists of an invokation of the command import.
This call has to leave the plugin in a state where another usage cycle can be run
without problems.
USAGE
To use a converter do
# Get the converter (single command here, not class)
package require the-converter-package
# Perform the conversion
set serial [theconverter convert $thegrammartext]
... process the result ...
To use a plugin FOO do
# 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 ...
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.
We distinguish between regular and canonical serializations. While a PEG may have more
than one regular serialization only exactly one of them will be canonical.
regular serialization
[1] The serialization of any PEG is a nested Tcl dictionary.
[2] This dictionary holds a single key, pt::grammar::peg, and its value. This
value holds the contents of the grammar.
[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
rules The value is a Tcl dictionary whose keys are the names of the
nonterminal symbols known to the grammar.
[1] Each nonterminal symbol may occur only once.
[2] The empty string is not a legal nonterminal symbol.
[3] The value for each symbol is a Tcl dictionary itself. The
relevant keys and their values in this dictionary are
is The value is the serialization of the parsing
expression describing the symbols sentennial structure,
as specified in the section PE serialization format.
mode The value can be one of three values specifying how a
parser should handle the semantic value produced by the
symbol.
value 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.
leaf 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.
void The nonterminal has no semantic value. Any ASTs
generated by the symbol's right hand side are
discarded (as well).
start The value is the serialization of the start parsing expression of the
grammar, as specified in the section PE serialization format.
[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.
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.
[1] The keys found in all the nested Tcl dictionaries are sorted in ascending
dictionary order, as generated by Tcl's builtin command lsort -increasing
-dict.
[2] The string representation of the value is the canonical representation of a
Tcl dictionary. I.e. it does not contain superfluous whitespace.
EXAMPLE
Assuming the following PEG for simple mathematical expressions
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;
then its canonical serialization (except for whitespace) is
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}
}
PE SERIALIZATION FORMAT
Here we specify the format used by the Parser Tools to serialize Parsing Expressions as
immutable values for transport, comparison, etc.
We distinguish between regular and canonical serializations. While a parsing expression
may have more than one regular serialization only exactly one of them will be canonical.
Regular serialization
Atomic Parsing Expressions
[1] The string epsilon is an atomic parsing expression. It matches the
empty string.
[2] The string dot is an atomic parsing expression. It matches any
character.
[3] The string alnum 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 string is.
[4] The string alpha is an atomic parsing expression. It matches any
Unicode alphabet character. This is a custom extension of PEs based
on Tcl's builtin command string is.
[5] The string ascii 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 string is.
[6] The string control is an atomic parsing expression. It matches any
Unicode control character. This is a custom extension of PEs based on
Tcl's builtin command string is.
[7] The string digit 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 string is.
[8] The string graph 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 string is.
[9] The string lower 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 string is.
[10] The string print 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 string is.
[11] The string punct is an atomic parsing expression. It matches any
Unicode punctuation character. This is a custom extension of PEs
based on Tcl's builtin command string is.
[12] The string space is an atomic parsing expression. It matches any
Unicode space character. This is a custom extension of PEs based on
Tcl's builtin command string is.
[13] The string upper 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 string is.
[14] The string wordchar 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
string is.
[15] The string xdigit is an atomic parsing expression. It matches any
hexadecimal digit character. This is a custom extension of PEs based
on Tcl's builtin command string is.
[16] The string ddigit is an atomic parsing expression. It matches any
decimal digit character. This is a custom extension of PEs based on
Tcl's builtin command regexp.
[17] The expression [list t x] is an atomic parsing expression. It matches
the terminal string x.
[18] The expression [list n A] is an atomic parsing expression. It matches
the nonterminal A.
Combined Parsing Expressions
[1] For parsing expressions e1, e2, ... the result of [list / e1 e2 ... ]
is a parsing expression as well. This is the ordered choice, aka
prioritized choice.
[2] For parsing expressions e1, e2, ... the result of [list x e1 e2 ... ]
is a parsing expression as well. This is the sequence.
[3] For a parsing expression e the result of [list * e] is a parsing
expression as well. This is the kleene closure, describing zero or
more repetitions.
[4] For a parsing expression e the result of [list + e] is a parsing
expression as well. This is the positive kleene closure, describing
one or more repetitions.
[5] For a parsing expression e the result of [list & e] is a parsing
expression as well. This is the and lookahead predicate.
[6] For a parsing expression e the result of [list ! e] is a parsing
expression as well. This is the not lookahead predicate.
[7] For a parsing expression e the result of [list ? e] is a parsing
expression as well. This is the optional input.
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.
[1] The string representation of the value is the canonical representation of a
pure Tcl list. I.e. it does not contain superfluous whitespace.
[2] Terminals are not encoded as ranges (where start and end of the range are
identical).
EXAMPLE
Assuming the parsing expression shown on the right-hand side of the rule
Expression <- Term (AddOp Term)*
then its canonical serialization (except for whitespace) is
{x {n Term} {* {x {n AddOp} {n Term}}}}
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 output 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>