Provided by: tcllib_1.19-dfsg-2_all 
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.
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>