pt::pe(n) Parser Tools pt::pe(n)______________________________________________________________________________NAME
pt::pe - Parsing Expression Serialization
SYNOPSIS
package require Tcl 8.5
package require pt::pe ?1?
package require char
::pt::pe verify serial ?canonvar?
::pt::pe verify-as-canonical serial
::pt::pe canonicalize serial
::pt::pe print serial
::pt::pe bottomup cmdprefix pe
cmdprefix pe op arguments
::pt::pe topdown cmdprefix pe
::pt::pe equal seriala serialb
::pt::pe epsilon
::pt::pe dot
::pt::pe alnum
::pt::pe alpha
::pt::pe ascii
::pt::pe control
::pt::pe digit
::pt::pe graph
::pt::pe lower
::pt::pe print
::pt::pe punct
::pt::pe space
::pt::pe upper
::pt::pe wordchar
::pt::pe xdigit
::pt::pe ddigit
::pt::pe terminal t
::pt::pe range ta tb
::pt::pe nonterminal nt
::pt::pe choice pe...
::pt::pe sequence pe...
::pt::pe repeat0 pe
::pt::pe repeat1 pe
::pt::pe optional pe
::pt::pe ahead pe
::pt::pe notahead 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 commands to work with the serializations of pars‐
ing expressions as managed by the Parser Tools, and specified in sec‐
tion PE serialization format.
This is a supporting package in the Core Layer of Parser Tools.
IMAGE: arch_core_support
API
::pt::pe verify serial ?canonvar?
This command verifies that the content of serial is a valid
serialization of a parsing expression and will throw an error if
that is not the case. The result of the command is the empty
string.
If the argument canonvar is specified it is interpreted as the
name of a variable in the calling context. This variable will be
written to if and only if serial is a valid regular serializa‐
tion. Its value will be a boolean, with True indicating that the
serialization is not only valid, but also canonical. False will
be written for a valid, but non-canonical serialization.
For the specification of serializations see the section PE seri‐
alization format.
::pt::pe verify-as-canonical serial
This command verifies that the content of serial is a valid
canonical serialization of a parsing expression and will throw
an error if that is not the case. The result of the command is
the empty string.
For the specification of canonical serializations see the sec‐
tion PE serialization format.
::pt::pe canonicalize serial
This command assumes that the content of serial is a valid regu‐
lar serialization of a parsing expression and will throw an
error if that is not the case.
It will then convert the input into the canonical serialization
of this parsing expression and return it as its result. If the
input is already canonical it will be returned unchanged.
For the specification of regular and canonical serializations
see the section PE serialization format.
::pt::pe print serial
This command assumes that the argument serial contains a valid
serialization of a parsing expression and returns a string con‐
taining that PE in a human readable form.
The exact format of this form is not specified and cannot be
relied on for parsing or other machine-based activities.
For the specification of serializations see the section PE seri‐
alization format.
::pt::pe bottomup cmdprefix pe
This command walks the parsing expression pe from the bottom up
to the root, invoking the command prefix cmdprefix for each par‐
tial expression. This implies that the children of a parsing
expression PE are handled before PE.
The command prefix has the signature
cmdprefix pe op arguments
I.e. it is invoked with the parsing expression pe the
walk is currently at, the op'erator in the pe, and the
operator's arguments.
The result returned by the command prefix replaces pe in
the parsing expression it was a child of, allowing trans‐
formations of the expression tree.
This also means that for all inner parsing expressions
the contents of arguments are the results of the command
prefix invoked for the children of this inner parsing
expression.
::pt::pe topdown cmdprefix pe
This command walks the parsing expression pe from the root down
to the leaves, invoking the command prefix cmdprefix for each
partial expression. This implies that the children of a parsing
expression PE are handled after PE.
The command prefix has the same signature as for bottomup, see
above.
The result returned by the command prefix is ignored.
::pt::pe equal seriala serialb
This command tests the two parsing expressions seriala and seri‐
alb for structural equality. The result of the command is a
boolean value. It will be set to true if the expressions are
identical, and false otherwise.
String equality is usable only if we can assume that the two
parsing expressions are pure Tcl lists.
::pt::pe epsilon
This command constructs the atomic parsing expression for
epsilon.
::pt::pe dot
This command constructs the atomic parsing expression for dot.
::pt::pe alnum
This command constructs the atomic parsing expression for alnum.
::pt::pe alpha
This command constructs the atomic parsing expression for alpha.
::pt::pe ascii
This command constructs the atomic parsing expression for ascii.
::pt::pe control
This command constructs the atomic parsing expression for con‐
trol.
::pt::pe digit
This command constructs the atomic parsing expression for digit.
::pt::pe graph
This command constructs the atomic parsing expression for graph.
::pt::pe lower
This command constructs the atomic parsing expression for lower.
::pt::pe print
This command constructs the atomic parsing expression for print.
::pt::pe punct
This command constructs the atomic parsing expression for punct.
::pt::pe space
This command constructs the atomic parsing expression for space.
::pt::pe upper
This command constructs the atomic parsing expression for upper.
::pt::pe wordchar
This command constructs the atomic parsing expression for word‐
char.
::pt::pe xdigit
This command constructs the atomic parsing expression for
xdigit.
::pt::pe ddigit
This command constructs the atomic parsing expression for
ddigit.
::pt::pe terminal t
This command constructs the atomic parsing expression for the
terminal symbol t.
::pt::pe range ta tb
This command constructs the atomic parsing expression for the
range of terminal symbols ta ... tb.
::pt::pe nonterminal nt
This command constructs the atomic parsing expression for the
nonterminal symbol nt.
::pt::pe choice pe...
This command constructs the parsing expression representing the
ordered or prioritized choice between the argument parsing
expressions. The first argument has the highest priority.
::pt::pe sequence pe...
This command constructs the parsing expression representing the
sequence of the argument parsing expression. The first argument
is the first element of the sequence.
::pt::pe repeat0 pe
This command constructs the parsing expression representing the
zero or more repetition of the argument parsing expression pe,
also known as the kleene closure.
::pt::pe repeat1 pe
This command constructs the parsing expression representing the
one or more repetition of the argument parsing expression pe,
also known as the positive kleene closure.
::pt::pe optional pe
This command constructs the parsing expression representing the
optionality of the argument parsing expression pe.
::pt::pe ahead pe
This command constructs the parsing expression representing the
positive lookahead of the argument parsing expression pe.
::pt::pe notahead pe
This command constructs the parsing expression representing the
negative lookahead of the argument parsing expression pe.
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(n)
