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pt::peg::import(n) Parser Tools pt::peg::import(n)
____________________________________________________________________________________________________________
NAME
pt::peg::import - PEG Import
SYNOPSIS
package require Tcl 8.5
package require snit
package require configuration
package require pt::peg
package require pluginmgr
package require pt::peg::import ?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
____________________________________________________________________________________________________________
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 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, con-tainer, container,
tainer, 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 grammars 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 serialization 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\IMPORT\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 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 docu-ments documents
ments the interaction 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 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 object-Name objectName
Name 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 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 import text text ?format?
This method takes the text and converts it from the specified format to the canonical serial-ization serialization
ization 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 serialization generated by the conver-sion conversion
sion 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 serial-ization serialization
ization format.
The plugin has to conform to the interface documented in the Parser Tools Import API specifi-cation. specification.
cation.
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
returns 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 being 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 include 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 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::peg::import(n)
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