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pt_import_api(i) Parser Tools pt_import_api(i)
____________________________________________________________________________________________________________
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 over-view overview
view provided by the Introduction to Parser Tools. This document is the entrypoint to the whole sys-tem system
tem 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 imple-ment implement
ment 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 con-verter converter
verter 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 pro-cessed. processed.
cessed.
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 opera-tion. operation.
tion.
[2] In case of success the contents of the included file, and the empty string oth-erwise. otherwise.
erwise.
[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 cur-rentfile currentfile
rentfile 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 reg-ular regular
ular 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 sym-bols symbols
bols 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 describ-ing describing
ing 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 non-terminal nonterminal
terminal 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 non-terminal, nonterminal,
terminal, 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 dictio-nary. dictionary.
nary. 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 <- '(' Expression ')' / (Factor (MulOp Factor)*) ;
MulOp <- '*' / '/' ;
Factor <- Term (AddOp Term)* ;
AddOp <- '+'/'-' ;
Term <- 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 {t (} {n Expression} {t )}} {x {n Factor} {* {x {n MulOp} {n Factor}}}}} mode value}
Factor {is {x {n Term} {* {x {n AddOp} {n Term}}}} 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 {n Number} 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 alpha-
bet 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 alpha-bet alphabet
bet 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 charac-ter character
ter below U0080. This is a custom extension of PEs based on Tcl's builtin com-mand command
mand string is.
[6] The string control is an atomic parsing expression. It matches any Unicode con-trol control
trol 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 print-ing printing
ing 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 lowercase
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 print-ing printing
ing 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 punctu-ation punctuation
ation character. This is a custom extension of PEs based on Tcl's builtin com-mand command
mand 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 uppercase
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 com-mand command
mand 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 reg-exp. regexp.
exp.
[17] The expression [list t x] is an atomic parsing expression. It matches the termi-nal terminal
nal string x.
[18] The expression [list n A] is an atomic parsing expression. It matches the non-terminal nonterminal
terminal A.
Combined Parsing Expressions
[1] For parsing expressions e1, e2, ... the result of [list / e1 e2 ... ] is a pars-ing parsing
ing 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 pars-ing parsing
ing 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 previ-ous previous
ous 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 <- '(' Expression ')'
/ Factor (MulOp Factor)*
then its canonical serialization (except for whitespace) is
{/ {x {t (} {n Expression} {t )}} {x {n Factor} {* {x {n MulOp} {n Factor}}}}}
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 SF Trackers [http://source -
forge.net/tracker/? group_id=12883]. Please also report any ideas for enhancements you may have for
either package and/or documentation.
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 pars-ing parsing
ing languages, transducer
CATEGORY
Parsing and Grammars
COPYRIGHT
Copyright (c) 2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>
pt 1 pt_import_api(i)
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