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
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>