Provided by: tcllib_1.21+dfsg-1_all 
NAME
pt::peg::to::cparam - PEG Conversion. Write CPARAM format
SYNOPSIS
package require Tcl 8.5
package require pt::peg::to::cparam ?1.1.2?
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 configuration of the
package.
pt::peg::to::cparam 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::cparam 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::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 command.
OPTIONS
The converter to C code recognizes the following configuration variables 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 processing. 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 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 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-varname.
@self@ To be replaced with the value of the option self-command.
@def@ To be replaced with the value of the option fun-qualifier.
@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 generated 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.
-comments boolean
A flag controlling the generation of code comments containing the original parsing
expression a parsing function is for. The default value is on.
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 configuration 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
-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. Further the options
-indent integer
-comments boolean
allow for the customization of the code indent (default none), and whether to generate
comments showing the parsing expressions a function is for (default on).
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 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
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>