NAME¶
pt::peg::export - PEG Export
SYNOPSIS¶
package require
Tcl 8.5
package require
snit
package require
configuration
package require
pt::peg
package require
pluginmgr
package require
pt::peg::export ?1?
::pt::peg::export objectName
objectName method ?
arg arg ...?
objectName destroy
objectName export serial serial ?
format?
objectName export object object ?
format?
objectName configuration names
objectName configuration get
objectName configuration set name ?
value?
objectName configuration unset pattern...
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 package provides a manager for parsing expression grammars, with each
instance handling a set of plugins for the export of them to other formats,
i.e. their conversion to, for example
nroff,
HTML, etc.
It resides in the Export section of the Core Layer of Parser Tools, and is one
of the three pillars the management of parsing expression grammars resides on.
IMAGE: arch_core_export
The other two pillars are, as shown above
- [1]
- PEG Import, and
- [2]
- PEG Storage
For information about the data structure which is the major input to the manager
objects provided by this package see the section
PEG serialization
format.
The plugin system of this class is based on the package
pluginmgr, and
configured to look for plugins using
- [1]
- the environment variable GRAMMAR_PEG_EXPORT_PLUGINS,
- [2]
- the environment variable GRAMMAR_PEG_PLUGINS,
- [3]
- the environment variable GRAMMAR_PLUGINS,
- [4]
- the path "~/.grammar/peg/export/plugin"
- [5]
- the path "~/.grammar/peg/plugin"
- [6]
- the path "~/.grammar/plugin"
- [7]
- the path "~/.grammar/peg/export/plugins"
- [8]
- the path "~/.grammar/peg/plugins"
- [9]
- the path "~/.grammar/plugins"
- [10]
- the registry entry
"HKEY_CURRENT_USER\SOFTWARE\GRAMMAR\PEG\EXPORT\PLUGINS"
- [11]
- the registry entry
"HKEY_CURRENT_USER\SOFTWARE\GRAMMAR\PEG\PLUGINS"
- [12]
- the registry entry
"HKEY_CURRENT_USER\SOFTWARE\GRAMMAR\PLUGINS"
The last three are used only when the package is run on a machine using the
Windows(tm) operating system.
The whole system is delivered with three predefined export plugins, namely
- container
- See PEG Export Plugin. To CONTAINER format for details.
- json
- See PEG Export Plugin. To JSON format for details.
- peg
- See PEG Export Plugin. To PEG format for details.
For readers wishing to write their own export plugin for some format, i.e.
plugin writers, reading and understanding the
Parser Tools Export
API specification is an absolute necessity, as it documents the
interaction between this package and its plugins in detail.
API¶
PACKAGE COMMANDS¶
- ::pt::peg::export objectName
- This command creates a new export manager object with an associated Tcl
command whose name is objectName. This object command is
explained in full detail in the sections Object command and
Object methods. The object command will be created under the
current namespace if the objectName is not fully qualified, and in
the specified namespace otherwise.
OBJECT COMMAND¶
All objects created by the
::pt::peg::export command have the following
general form:
- objectName method ?arg arg ...?
- The method method and its arg'uments determine the exact
behavior of the command. See section Object methods for the
detailed specifications.
OBJECT METHODS¶
- objectName destroy
- This method destroys the object it is invoked for.
- objectName export serial serial ?format?
- This method takes the canonical serialization of a parsing expression
grammar stored in serial and converts it to the specified
format, using the export plugin for the format. This will fail with
an error if no plugin could be found for the format. The string generated
by the conversion process is returned as the result of this method.
If no format is specified the method defaults to text.
The specification of what a canonical serialization is can be found
in the section PEG serialization format.
The plugin has to conform to the interface documented in the Parser Tools
Export API specification.
- objectName export object object ?format?
- This method is a convenient wrapper around the export serial method
described by the previous item. It expects that object is an object
command supporting a serialize method returning the canonical
serialization of a parsing expression grammar. It invokes that method,
feeds the result into export serial and returns the resulting
string as its own result.
- objectName configuration names
- This method returns a list containing the names of all configuration
options currently known to the object.
- objectName configuration get
- This method returns a dictionary containing the names and values of all
configuration options currently known to the object.
- objectName configuration set name ?value?
- This method sets the configuration option name to the specified
value and returns the new value of the option.
If no value is specified it simply returns the current value, without
changing it.
Note that these configuration options and their values are simply passed to
a plugin when the actual export is performed. It is the plugin which
checks the validity, not the manager.
- objectName configuration unset pattern...
- This method unsets all configuration options matching the specified glob
patterns. If no pattern is specified it will unset all currently
defined configuration options.
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}
}
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.
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>