Provided by: tcllib_1.21+dfsg-1_all 
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
________________________________________________________________________________________________________________
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 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 documents 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 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 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
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 serialization 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 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 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>