[comment {-*- text -*- doctools manpage}]
[vset VERSION 1.2.0]
[manpage_begin pt_peg_op i [vset VERSION]]
[include include/module.inc]
[titledesc {Parser Tools PE Grammar Utility Operations}]
[require pt::peg::op [opt [vset VERSION]]]
[description]
[include include/ref_intro.inc]

This package provides a number of utility commands manipulating a PE
grammar (container) in various ways.

[section API]

[list_begin definitions]
[comment ---------------------------------------------------------------------]
[call [cmd ::peg::peg::op] [method called] [arg container]]

This command determines the static call structure for the nonterminal
symbols of the grammar stored in the [arg container].

[para] 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.

[para] The grammar in the container is not modified.

[para] The [arg container] instance has to expose a method API as is
provided by the package [package pt::peg::container].

[comment ---------------------------------------------------------------------]
[call [cmd ::peg::peg::op] [method dechain] [arg 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.

[para][example {
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    |
}]

[para] The result of the command is the empty string.

[para] The grammar in the container is directly modified. If that is
not wanted, a copy of the original container has to be used.

[para] The [arg container] instance has to expose a method API as is
provided by the package [package pt::peg::container].

[comment ---------------------------------------------------------------------]
[call [cmd ::peg::peg::op] [method {drop unreachable}] [arg container]]

This command removes all symbols from the grammar which are not
[method reachable].

[para] The result of the command is the empty string.

[para] The grammar in the container is directly modified. If that is
not wanted, a copy of the original container has to be used.

[para] The [arg container] instance has to expose a method API as is
provided by the package [package pt::peg::container].

[comment ---------------------------------------------------------------------]
[call [cmd ::peg::peg::op] [method {drop unrealizable}] [arg container]]

This command removes all symbols from the grammar which are not
[method realizable].

[para] The result of the command is the empty string.

[para] The grammar in the container is directly modified. If that is
not wanted, a copy of the original container has to be used.

[para] The [arg container] instance has to expose a method API as is
provided by the package [package pt::peg::container].

[comment ---------------------------------------------------------------------]
[call [cmd ::peg::peg::op] [method flatten] [arg container]]

This command flattens (see [package pt::pe::op]) all expressions in
the grammar, i.e. the start expression and the right hand sides of all
nonterminal symbols.

[para] The result of the command is the empty string.

[para] The grammar in the container is directly modified. If that is
not wanted, a copy of the original container has to be used.

[para] The [arg container] instance has to expose a method API as is
provided by the package [package pt::peg::container].

[comment ---------------------------------------------------------------------]
[call [cmd ::peg::peg::op] [method minimize] [arg container]]

This command reduces the provided grammar by applying most of the other methods of this package.

[para] 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.

[para] The result of the command is the empty string.

[para] The grammar in the container is directly modified. If that is
not wanted, a copy of the original container has to be used.

[para] The [arg container] instance has to expose a method API as is
provided by the package [package pt::peg::container].

[comment ---------------------------------------------------------------------]
[call [cmd ::peg::peg::op] [method modeopt] [arg container]]

This command optimizes the semantic modes of non-terminal symbols
according to the two rules below.

[list_begin enumerated]
[enum]  If a symbol X with mode [const value] calls no other symbols,
        i.e. uses only terminal symbols in whatever combination, then
	this can be represented simpler by using mode [const leaf].

[enum]	If a symbol X is only called from symbols with modes
	[const leaf] or [const void] then this symbol should have mode
	[const void] also, as any AST it could generate will be
	discarded anyway.
[list_end]

[para] The result of the command is the empty string.

[para] The grammar in the container is directly modified. If that is
not wanted, a copy of the original container has to be used.

[para] The [arg container] instance has to expose a method API as is
provided by the package [package pt::peg::container].

[comment ---------------------------------------------------------------------]
[call [cmd ::peg::peg::op] [method reachable] [arg 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 [method called] and the
symbol's right hand sides, beginning with the start expression.

[para] The result of the command is the list of reachable symbols.

[para] The grammar in the container is not modified.

[para] The [arg container] instance has to expose a method API as is
provided by the package [package pt::peg::container].

[comment ---------------------------------------------------------------------]
[call [cmd ::peg::peg::op] [method realizable] [arg 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.

[para] The result of the command is the list of realizable symbols.

[para] The grammar in the container is not modified.

[para] The [arg container] instance has to expose a method API as is
provided by the package [package pt::peg::container].

[list_end]

[include include/feedback.inc]
[manpage_end]
