pt::peg::to::cparam(n) Parser Tools pt::peg::to::cparam(n)______________________________________________________________________________NAME
pt::peg::to::cparam - PEG Conversion. Write CPARAM format
SYNOPSIS
package require Tcl 8.5
package require pt::peg::to::cparam ?1.0.1?
pt::peg::to::cparam reset
pt::peg::to::cparam configure
pt::peg::to::cparam configure option
pt::peg::to::cparam configure option value...
pt::peg::to::cparam 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 CPARAM 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::cparam 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::cparam reset
This command resets the configuration of the package to its
default settings.
pt::peg::to::cparam configure
This command returns a dictionary containing the current config‐
uration of the package.
pt::peg::to::cparam configure option
This command returns the current value of the specified configu‐
ration option of the package. For the set of legal options,
please read the section Options.
pt::peg::to::cparam configure option value...
This command sets the given configuration options of the pack‐
age, to the specified values. For the set of legal options,
please read the section Options.
pt::peg::to::cparam 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 CPARAM markup
encoding the grammar, per the current package configuration.
The created string is then returned as the result of the com‐
mand.
OPTIONS
The converter to C code recognizes the following configuration vari‐
ables and changes its behaviour as they specify.
-file string
The value of this option is the name of the file or other entity
from which the grammar came, for which the command is run. The
default value is unknown.
-name string
The value of this option is the name of the grammar we are pro‐
cessing. The default value is a_pe_grammar.
-user string
The value of this option is the name of the user for which the
command is run. The default value is unknown.
-template string
The value of this option is a string into which to put the gen‐
erated 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 option -user.
@format@
To be replaced with the the constant C/PARAM.
@file@ To be replaced with the value of the option -file.
@name@ To be replaced with the value of the option -name.
@code@ To be replaced with the generated Tcl code.
The following options are special, in that they will occur within the
generated code, and are replaced there as well.
@statedecl@
To be replaced with the value of the option state-decl.
@stateref@
To be replaced with the value of the option state-ref.
@strings@
To be replaced with the value of the option string-var‐
name.
@self@ To be replaced with the value of the option self-command.
@def@ To be replaced with the value of the option fun-quali‐
fier.
@ns@ To be replaced with the value of the option namespace.
@main@ To be replaced with the value of the option main.
@prelude@
To be replaced with the value of the option prelude.
-state-decl string
A C string representing the argument declaration to use in the
generated parsing functions to refer to the parsing state. In
essence type and argument name. The default value is the string
RDE_PARAM p.
-state-ref string
A C string representing the argument named used in the generated
parsing functions to refer to the parsing state. The default
value is the string p.
-self-command string
A C string representing the reference needed to call the gener‐
ated parser function (methods ...) from another parser fonction,
per the chosen framework (template). The default value is the
empty string.
-fun-qualifier string
A C string containing the attributes to give to the generated
functions (methods ...), per the chosen framework (template).
The default value is static.
-namespace string
The name of the C namespace the parser functions (methods, ...)
shall reside in, or a general prefix to add to the function
names. The default value is the empty string.
-main string
The name of the main function (method, ...) to be called by the
chosen framework (template) to start parsing input. The default
value is __main.
-string-varname string
The name of the variable used for the table of strings used by
the generated parser, i.e. error messages, symbol names, etc.
The default value is p_string.
-prelude string
A snippet of code to be inserted at the head of each generated
parsing function. 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 an adjunct package is provided, containing a
canned configuration which will generate immediately useful full
parsers. It is
pt::cparam::configuration::critcl
Generated parsers are embedded into a Critcl-based framework.
C/PARAM CODE REPRESENTATION OF PARSING EXPRESSION GRAMMARS
The c format is executable code, a parser for the grammar. The parser
implementation is written in C and can be tweaked to the users' needs
through a multitude of options.
The critcl format, for example, is implemented as a canned configura‐
tion of these options on top of the generator for c.
The bulk of such a framework has to be specified through the option
-template. The additional options
-fun-qualifier string
-indent integer
-main string
-namespace string
-prelude string
-self-command string
-state-decl string
-state-ref string
-string-varname string
provide code snippets which help to glue framework and generated code
together. Their placeholders are in the generated code.
EXAMPLE
We are forgoing an example of this representation, with apologies. It
would be way to large for this document.
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
abstract syntax tree consist‐
ing 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
abstract syntax tree consist‐
ing 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 <- '(' 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 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
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 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 <- '(' 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://sourceforge.net/tracker/?group_id=12883].
Please also report any ideas for enhancements you may have for either
package and/or documentation.
KEYWORDS
CPARAM, EBNF, LL(k), PEG, 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>
pt 1.0.1 pt::peg::to::cparam(n)
