pt::pe::op(n) Parser Tools pt::pe::op(n)______________________________________________________________________________NAME
pt::pe::op - Parsing Expression Utilities
SYNOPSIS
package require Tcl 8.5
package require pt::pe::op ?1?
package require pt::pe ?1?
package require struct::set
::pt::pe::op drop dropset pe
::pt::pe::op rename nt ntnew pe
::pt::pe::op called pe
::pt::pe::op flatten pe
::pt::pe::op fusechars pe
_________________________________________________________________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 provides additional commands to work with the serializa‐
tions of parsing expressions as managed by the PEG and related pack‐
ages, and specified in section PE serialization format.
This is an internal package, for use by the higher level packages han‐
dling PEGs, their conversion into and out of various other formats, or
other uses.
API
::pt::pe::op drop dropset pe
This command removes all occurences of any of the nonterminals
symbols in the set dropset from the parsing expression pe, and
simplifies it. This may result in the expression becoming
"epsilon", i.e. matching nothing.
::pt::pe::op rename nt ntnew pe
This command renames all occurences of the nonterminal nt in the
parsing expression pe into ntnew.
::pt::pe::op called pe
This command extracts the set of all nonterminal symbols used,
i.e. 'called', in the parsing expression pe.
::pt::pe::op flatten pe
This command transforms the parsing expression by eliminating
sequences nested in sequences, and choices in choices, lifting
the children of the nested expression into the parent. It fur‐
ther eliminates all sequences and choices with only one child,
as these are redundant.
The resulting parsing expression is returned as the result of
the command.
::pt::pe::op fusechars pe
This command transforms the parsing expression by fusing adja‐
cent terminals in sequences and adjacent terminals and ranges in
choices, it (re)constructs highlevel strings and character
classes.
The resulting pseudo-parsing expression is returned as the
result of the command and may contain the pseudo-operators str
for character sequences, aka strings, and cl for character
choices, aka character classes.
The result is called a pseudo-parsing expression because it is
not a true parsing expression anymore, and will fail a check
with ::pt::peg verify if the new pseudo-operators are present in
the result, but is otherwise of sound structure for a parsing
expression. Notably, the commands ::pt::peg bottomup and
::pt::peg topdown will process them without trouble.
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
EBNF, LL(k), PEG, TDPL, context-free languages, expression, grammar,
matching, parser, parsing expression, parsing expression grammar, push
down automaton, recursive descent, state, top-down parsing languages,
transducer
CATEGORY
Parsing and Grammars
COPYRIGHT
Copyright (c) 2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>
pt 1 pt::pe::op(n)
