pt::peg::import(3tcl) Parser Tools pt::peg::import(3tcl)
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NAME
pt::peg::import - PEG Import
SYNOPSIS
package require Tcl 8.5
package require Tcl 8.5
package require snit
package require fileutil::paths
package require pt::peg
package require pluginmgr
package require pt::peg::import ?1.0.1?
::pt::peg::import objectName
objectName method ?arg arg ...?
objectName destroy
objectName import text text ?format?
objectName import file path ?format?
objectName import object text object text ?format?
objectName import object file object path ?format?
objectName includes
objectName include add path
objectName include remove path
objectName include clear
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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 import of them from
other formats, i.e. their conversion from, for example peg, container,
json, etc.
It resides in the Import section of the Core Layer of Parser Tools, and
is one of the three pillars the management of parsing expression gram-
mars resides on.
IMAGE: arch_core_import
The other two pillars are, as shown above
[1] PEG Export, and
[2] PEG Storage
For information about the data structure which is the major output of
the manager objects provided by this package see the section PEG seri-
alization format.
The plugin system of our class is based on the package pluginmgr, and
configured to look for plugins using
[1] the environment variable GRAMMAR_PEG_IMPORT_PLUGINS,
[2] the environment variable GRAMMAR_PEG_PLUGINS,
[3] the environment variable GRAMMAR_PLUGINS,
[4] the path "~/.grammar/peg/import/plugin"
[5] the path "~/.grammar/peg/plugin"
[6] the path "~/.grammar/plugin"
[7] the path "~/.grammar/peg/import/plugins"
[8] the path "~/.grammar/peg/plugins"
[9] the path "~/.grammar/plugins"
[10] the registry entry "HKEY_CURRENT_USER\SOFTWARE\GRAMMAR\PEG\IM-
PORT\PLUGINS"
[11] the registry entry "HKEY_CURRENT_USER\SOFTWARE\GRAMMAR\PEG\PLUG-
INS"
[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 import plugins,
namely
container
See PEG Import Plugin. From CONTAINER format for details.
json See PEG Import Plugin. From JSON format for details.
peg See PEG Import Plugin. From PEG format for details.
For readers wishing to write their own import plugin for some format,
i.e. plugin writers, reading and understanding the Parser Tools Impport
API specification is an absolute necessity, as it documents the inter-
action between this package and its plugins in detail.
API
PACKAGE COMMANDS
::pt::peg::import objectName
This command creates a new import manager object with an associ-
ated 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::import command have the following
general form:
objectName method ?arg arg ...?
The method method and its arg'uments determine the exact behav-
ior 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 import text text ?format?
This method takes the text and converts it from the specified
format to the canonical serialization of a parsing expression
grammar using the import plugin for the format. An error is
thrown if no plugin could be found for the format. The serial-
ization 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 Import API specification.
objectName import file path ?format?
This method is a convenient wrapper around the import text
method described by the previous item. It reads the contents of
the specified file into memory, feeds the result into import
text and returns the resulting serialization as its own result.
objectName import object text object text ?format?
This method is a convenient wrapper around the import text
method described by the previous item. It expects that object
is an object command supporting a deserialize method expecting
the canonical serialization of a parsing expression grammar. It
imports the text using import text and then feeds the resulting
serialization into the object via deserialize. This method re-
turns the empty string as it result.
objectName import object file object path ?format?
This method behaves like import object text, except that it
reads the text to convert from the specified file instead of be-
ing given it as argument.
objectName includes
This method returns a list containing the currently specified
paths to use to search for include files when processing input.
The order of paths in the list corresponds to the order in which
they are used, from first to last, and also corresponds to the
order in which they were added to the object.
objectName include add path
This methods adds the specified path to the list of paths to use
to search for include files when processing input. The path is
added to the end of the list, causing it to be searched after
all previously added paths. The result of the command is the
empty string.
The method does nothing if the path is already known.
objectName include remove path
This methods removes the specified path from the list of paths
to use to search for include files when processing input. The
result of the command is the empty string.
The method does nothing if the path is not known.
objectName include clear
This method clears the list of paths to use to search for in-
clude files when processing input. The result of the command is
the empty string.
PEG SERIALIZATION FORMAT
Here we specify the format used by the Parser Tools to serialize Pars-
ing 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 expres-
sion. 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 dictio-
nary 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 serial-
ization format.
mode The value can be one of three values
specifying how a parser should han-
dle the semantic value produced by
the symbol.
value The semantic value of the
nonterminal symbol is an ab-
stract 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 chil-
dren.
leaf The semantic value of the
nonterminal symbol is an ab-
stract 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 seman-
tic value. Any ASTs generated
by the symbol's right hand
side are discarded (as well).
start The value is the serialization of the start pars-
ing expression of the grammar, as specified in the
section PE serialization format.
[4] The terminal symbols of the grammar are specified implic-
itly 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 spec-
ified 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 con-
tain 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 Pars-
ing 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 expres-
sion. 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 charac-
ter. 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 expres-
sion. 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 charac-
ter. 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, includ-
ing 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 charac-
ter. This is a custom extension of PEs based on
Tcl's builtin command string is.
[14] The string wordchar is an atomic parsing expres-
sion. It matches any Unicode word character. This
is any alphanumeric character (see alnum), and any
connector punctuation characters (e.g. under-
score). 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 ex-
pression. It matches the terminal string x.
[18] The expression [list n A] is an atomic parsing ex-
pression. 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 repeti-
tions.
[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 for-
mat 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 con-
tain 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 out-
put 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>
tcllib 1.0.1 pt::peg::import(3tcl)