NAME¶
pt_peg_op - Parser Tools PE Grammar Utility Operations
SYNOPSIS¶
package require
Tcl 8.5
package require
pt::peg::op 1.0.1
::peg::peg::op called container
::peg::peg::op dechain container
::peg::peg::op drop unreachable container
::peg::peg::op drop unrealizable container
::peg::peg::op flatten container
::peg::peg::op minimize container
::peg::peg::op modeopt container
::peg::peg::op reachable container
::peg::peg::op realizable container
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 a number of utility commands manipulating a PE grammar
(container) in various ways.
API¶
- ::peg::peg::op called container
- This command determines the static call structure for the nonterminal
symbols of the grammar stored in the container.
The result of the command is a dictionary mapping from each symbol to the
symbols it calls. The empty string is the key used to represent the start
expression of the grammar.
The grammar in the container is not modified.
The container instance has to expose a method API as is provided by
the package pt::peg::container.
- ::peg::peg::op dechain container
- This command simplifies all symbols which just chain to a different symbol
by inlining the right hand side of the called symbol in its callers. This
works if and only the modes match properly, per the decision table below.
caller called | dechain | notes
--------------+---------+-----------------------
value value | yes | value is passed
value leaf | yes | value is passed
value void | yes | caller is implied void
leaf value | no | generated value was discarded, inlined would not. called may be implied void.
leaf leaf | no | s.a.
leaf void | no | s.a.
void value | no | caller drops value, inlined would not.
void leaf | no | s.a.
void void | yes |
The result of the command is the empty string.
The grammar in the container is directly modified. If that is not wanted, a copy
of the original container has to be used.
The
container instance has to expose a method API as is provided by the
package
pt::peg::container.
- ::peg::peg::op drop unreachable container
- This command removes all symbols from the grammar which are not
reachable.
The result of the command is the empty string.
The grammar in the container is directly modified. If that is not wanted, a
copy of the original container has to be used.
The container instance has to expose a method API as is provided by
the package pt::peg::container.
- ::peg::peg::op drop unrealizable container
- This command removes all symbols from the grammar which are not
realizable.
The result of the command is the empty string.
The grammar in the container is directly modified. If that is not wanted, a
copy of the original container has to be used.
The container instance has to expose a method API as is provided by
the package pt::peg::container.
- ::peg::peg::op flatten container
- This command flattens (see pt::pe::op) all expressions in the
grammar, i.e. the start expression and the right hand sides of all
nonterminal symbols.
The result of the command is the empty string.
The grammar in the container is directly modified. If that is not wanted, a
copy of the original container has to be used.
The container instance has to expose a method API as is provided by
the package pt::peg::container.
- ::peg::peg::op minimize container
- This command reduces the provided grammar by applying most of the other
methods of this package.
After flattening the expressions it removes unreachable and unrealizable
symbols, flattens the expressions again, then optimizes the symbol modes
before collapsing symbol chains as much as possible.
The result of the command is the empty string.
The grammar in the container is directly modified. If that is not wanted, a
copy of the original container has to be used.
The container instance has to expose a method API as is provided by
the package pt::peg::container.
- ::peg::peg::op modeopt container
- This command optimizes the semantic modes of non-terminal symbols
according to the two rules below.
- [1]
- If a symbol X with mode value calls no other symbols, i.e. uses
only terminal symbols in whatever combination, then this can be
represented simpler by using mode leaf.
- [2]
- If a symbol X is only called from symbols with modes leaf or
void then this symbol should have mode void also, as any AST
it could generate will be discarded anyway.
The result of the command is the empty string.
The grammar in the container is directly modified. If that is not wanted, a copy
of the original container has to be used.
The
container instance has to expose a method API as is provided by the
package
pt::peg::container.
- ::peg::peg::op reachable container
- This command computes the set of all nonterminal symbols which are
reachable from the start expression of the grammar. This is essentially
the transitive closure over called and the symbol's right hand
sides, beginning with the start expression.
The result of the command is the list of reachable symbols.
The grammar in the container is not modified.
The container instance has to expose a method API as is provided by
the package pt::peg::container.
- ::peg::peg::op realizable container
- This command computes the set of all nonterminal symbols which are
realizable, i.e. can derive pure terminal phrases. This is done
iteratively, starting with state unrealizable for all and any, and then
updating all symbols which are realizable, propagating changes, until
nothing changes any more.
The result of the command is the list of realizable symbols.
The grammar in the container is not modified.
The container instance has to expose a method API as is provided by
the package pt::peg::container.
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>
