pt::peg::export::container(3tcl) Parser Tools pt::peg::export::container(3tcl)
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NAME
pt::peg::export::container - PEG Export Plugin. Write CONTAINER format
SYNOPSIS
package require Tcl 8.5
package require pt::peg::export::container ?1?
package require pt::peg::to::container
export serial configuration
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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 implements the parsing expression grammar export plugin
for the generation of CONTAINER markup.
It resides in the Export section of the Core Layer of Parser Tools and
is intended to be used by pt::peg::export, the export manager, sitting
between it and the corresponding core conversion functionality provided
by pt::peg::to::container.
IMAGE: arch_core_eplugins
While the direct use of this package with a regular interpreter is pos-
sible, this is strongly disrecommended and requires a number of contor-
tions to provide the expected environment. The proper way to use this
functionality depends on the situation:
[1] In an untrusted environment the proper access is through the
package pt::peg::export and the export manager objects it pro-
vides.
[2] In a trusted environment however simply use the package
pt::peg::to::container and access the core conversion function-
ality directly.
API
The API provided by this package satisfies the specification of the
Plugin API found in the Parser Tools Export API specification.
export serial configuration
This command takes the canonical serialization of a parsing ex-
pression grammar, as specified in section PEG serialization for-
mat, and contained in serial, the configuration, a dictionary,
and generates CONTAINER markup encoding the grammar. The cre-
ated string is then returned as the result of the command.
CONFIGURATION
The CONTAINER export plugin recognizes the following configuration
variables and changes its behaviour as they specify.
enum mode
The value of this configuration variable controls which methods
of pt::peg instances the plugin will use to specify the grammar.
There are two legal values
bulk In this mode the methods start, add, modes, and rules are
used to specify the grammar in a bulk manner, i.e. as a
set of nonterminal symbols, and two dictionaries mapping
from the symbols to their semantic modes and parsing ex-
pressions.
This mode is the default.
incremental
In this mode the methods start, add, mode, and rule are
used to specify the grammar piecemal, with each nontermi-
nal having its own block of defining commands.
string template
If this configuration variable is set it is assumed to contain a
string into which to put the generated code and other configura-
tion data. The various locations are expected to be specified
with the following placeholders:
@user@ To be replaced with the value of the configuration vari-
able user.
@format@
To be replaced with the the constant CONTAINER.
@file@ To be replaced with the value of the configuration vari-
able file.
@name@ To be replaced with the value of the configuration vari-
able name.
@mode@ To be replaced with the value of the configuration vari-
able mode.
@code@ To be replaced with the generated code.
If this configuration variable is not set, or empty, then the plugin
falls back to a standard template, which is defined as "@code@".
Note that this plugin may ignore the standard configuration variables
user, format, file, and their values, depending on the chosen template.
The content of the standard configuration variable name, if set, is
used as name of the grammar in the output. Otherwise the plugin falls
back to the default name a_pe_grammar.
GRAMMAR CONTAINER
The container format is another form of describing parsing expression
grammars. While data in this format is executable it does not consti-
tute a parser for the grammar. It always has to be used in conjunction
with the package pt::peg::interp, a grammar interpreter.
The format represents grammars by a snit::type, i.e. class, whose in-
stances are API-compatible to the instances of the pt::peg::container
package, and which are preloaded with the grammar in question.
It has no direct formal specification beyond what was said above.
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;
one possible CONTAINER serialization for it is
snit::type a_pe_grammar {
constructor {} {
install myg using pt::peg::container ${selfns}::G
$myg start {n Expression}
$myg add AddOp Digit Expression Factor MulOp Number Sign Term
$myg modes {
AddOp value
Digit value
Expression value
Factor value
MulOp value
Number value
Sign value
Term value
}
$myg rules {
AddOp {/ {t -} {t +}}
Digit {/ {t 0} {t 1} {t 2} {t 3} {t 4} {t 5} {t 6} {t 7} {t 8} {t 9}}
Expression {/ {x {t \50} {n Expression} {t \51}} {x {n Factor} {* {x {n MulOp} {n Factor}}}}}
Factor {x {n Term} {* {x {n AddOp} {n Term}}}}
MulOp {/ {t *} {t /}}
Number {x {? {n Sign}} {+ {n Digit}}}
Sign {/ {t -} {t +}}
Term {n Number}
}
return
}
component myg
delegate method * to myg
}
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
CONTAINER, EBNF, LL(k), PEG, TDPL, context-free languages, export, ex-
pression, grammar, matching, parser, parsing expression, parsing ex-
pression grammar, plugin, push down automaton, recursive descent, seri-
alization, state, top-down parsing languages, transducer
CATEGORY
Parsing and Grammars
COPYRIGHT
Copyright (c) 2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>
tcllib 1 pt::peg::export::container(3tcl)