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 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.
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
- -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.
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
Trackers [
http://core.tcl.tk/tcllib/reportlist]. 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>