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 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.
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¶
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>