pt_peg_op(3tcl) Parser Tools pt_peg_op(3tcl)
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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
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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 non-
terminal symbols of the grammar stored in the container.
The result of the command is a dictionary mapping from each sym-
bol 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 dif-
ferent symbol by inlining the right hand side of the called sym-
bol in its callers. This works if and only the modes match prop-
erly, 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 un-
realizable symbols, flattens the expressions again, then opti-
mizes 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 sym-
bols 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, propa-
gating 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 out-
put 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)