Provided by: tcllib_1.21+dfsg-1_all 
NAME
pt_peg_op - Parser Tools PE Grammar Utility Operations
SYNOPSIS
package require Tcl 8.5
package require pt::peg::op ?1.1.0?
::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.
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
CATEGORY
Parsing and Grammars
COPYRIGHT
Copyright (c) 2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>
tcllib 1.1.0 pt_peg_op(3tcl)