Ubuntu Manpage: pt::pe - Parsing Expression Serialization

NAME

       pt::pe - Parsing Expression Serialization

SYNOPSIS

       package require Tcl  8.5

       package require pt::pe  ?1.0.1?

       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 parsing expressions as
       managed by the Parser Tools, and specified in section 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 serialization. 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 serialization 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 section PE serialization
format.

::pt::pe canonicalize serial
This command assumes that the content of serial is a valid regular 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 containing 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 serialization 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 partial 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 transformations 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 serialb 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 control.

::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 wordchar.

::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 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

       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

COPYRIGHT

       Copyright (c) 2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>