NAME¶
pt::peg::to::tclparam - PEG Conversion. Write TCLPARAM format
SYNOPSIS¶
package require
Tcl 8.5
package require
pt::peg::to::tclparam ?1?
pt::peg::to::tclparam reset
pt::peg::to::tclparam configure
pt::peg::to::tclparam configure option
pt::peg::to::tclparam configure option value...
pt::peg::to::tclparam convert serial
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 converter from parsing expression grammars to
TCLPARAM markup.
It resides in the Export section of the Core Layer of Parser Tools, and can be
used either directly with the other packages of this layer, or indirectly
through the export manager provided by
pt::peg::export. The latter is
intented for use in untrusted environments and done through the corresponding
export plugin
pt::peg::export::tclparam sitting between converter and
export manager.
IMAGE: arch_core_eplugins
API¶
The API provided by this package satisfies the specification of the Converter
API found in the
Parser Tools Export API specification.
- pt::peg::to::tclparam reset
- This command resets the configuration of the package to its
default settings.
- pt::peg::to::tclparam configure
- This command returns a dictionary containing the current
configuration of the package.
- pt::peg::to::tclparam configure
option
- This command returns the current value of the specified
configuration option of the package. For the set of legal options,
please read the section Options.
- pt::peg::to::tclparam configure option
value...
- This command sets the given configuration options of
the package, to the specified values. For the set of legal options,
please read the section Options.
- pt::peg::to::tclparam convert
serial
- This command takes the canonical serialization of a parsing
expression grammar, as specified in section PEG serialization
format, and contained in serial, and generates TCLPARAM markup
encoding the grammar, per the current package configuration. The created
string is then returned as the result of the command.
OPTIONS¶
The converter to Tcl/PARAM markup recognizes the following configuration
variables and changes its behaviour as they specify.
- -template string
- The value of this configuration variable is a string into
which to put the generated text and the other configuration settings. The
various locations for user-data are expected to be specified with the
placeholders listed below. The default value is "
@code@".
- @user@
- To be replaced with the value of the configuration variable
-user.
- @format@
- To be replaced with the the constant Tcl/PARAM.
- @file@
- To be replaced with the value of the configuration variable
-file.
- @name@
- To be replaced with the value of the configuration variable
-name.
- @code@
- To be replaced with the generated Tcl code.
- The following configuration variables are special, in that
they will occur within the generated code, and are replaced there as
well.
- @runtime@
- To be replaced with the value of the configuration variable
runtime-command.
- @self@
- To be replaced with the value of the configuration variable
self-command.
- @def@
- To be replaced with the value of the configuration variable
proc-command.
- @ns@
- To be replaced with the value of the configuration variable
namespace.
- @main@
- To be replaced with the value of the configuration variable
main.
- @prelude@
- To be replaced with the value of the configuration variable
prelude.
- -name string
- The value of this configuration variable is the name of the
grammar for which the conversion is run. The default value is
a_pe_grammar.
- -user string
- The value of this configuration variable is the name of the
user for which the conversion is run. The default value is
unknown.
- -file string
- The value of this configuration variable is the name of the
file or other entity from which the grammar came, for which the conversion
is run. The default value is unknown.
- -runtime-command string
- A Tcl string representing the Tcl command or reference to
it used to call PARAM instruction from parser procedures, per the chosen
framework (template). The default value is the empty string.
- -self-command string
- A Tcl string representing the Tcl command or reference to
it used to call the parser procedures (methods ...) from another parser
procedure, per the chosen framework (template). The default value is the
empty string.
- -proc-command string
- The name of the Tcl command used to define procedures
(methods ...), per the chosen framework (template). The default value is
proc.
- -namespace string
- The name of the namespace the parser procedures (methods,
...) shall reside in, including the trailing '::' needed to separate it
from the actual procedure name. The default value is ::.
- -main string
- The name of the main procedure (method, ...) to be called
by the chosen framework (template) to start parsing input. The default
value is __main.
- -prelude string
- A snippet of code to be insert at the head of each
generated parsing command. The default value is the empty string.
- -indent integer
- The number of characters to indent each line of the
generated code by. The default value is 0.
While the high parameterizability of this converter, as shown by the multitude
of options it supports, is an advantage to the advanced user, allowing her to
customize the output of the converter as needed, a novice user will likely not
see the forest for the trees.
To help these latter users two adjunct packages are provided, each containing a
canned configuration which will generate immediately useful full parsers.
These are
- pt::tclparam::configuration::snit
- Generated parsers are classes based on the snit
package, i.e. snit::type's.
- pt::tclparam::configuration::tcloo
- Generated parsers are classes based on the OO
package.
TCL/PARAM CODE REPRESENTATION OF PARSING EXPRESSION GRAMMARS¶
The Tcl/PARAM representation of parsing expression grammars is Tcl code whose
execution will parse input per the grammar. The code is based on the virtual
machine documented in the
PackRat Machine Specification, using its
instructions and a few more to handle control flow.
Note that the generated code by itself is not functional. It expects to be
embedded into a framework which provides services like the PARAM state,
implementations for the PARAM instructions, etc. The bulk of such a framework
has to be specified through the option
-template. The additional
options
- -indent integer
- -main string
- -namespace string
- -prelude string
- -proc-command string
- -runtime-command string
- -self-command string
provide code snippets which help to glue framework and generated code together.
Their placeholders are in the
generated code.
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
SF Trackers [
http://sourceforge.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, TCLPARAM, TDPL, context-free languages, conversion,
expression, format conversion, grammar, matching, parser, parsing expression,
parsing expression grammar, push down automaton, recursive descent,
serialization, state, top-down parsing languages, transducer
CATEGORY¶
Parsing and Grammars
COPYRIGHT¶
Copyright (c) 2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>