1pt_peg_op(i) Parser Tools pt_peg_op(i)
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6
8 pt_peg_op - Parser Tools PE Grammar Utility Operations
9
11 package require Tcl 8.5
12 package require pt::peg::op ?1.1.0?
14 ::peg::peg::op called container
16 ::peg::peg::op dechain container
18 ::peg::peg::op drop unreachable container
20 ::peg::peg::op drop unrealizable container
22 ::peg::peg::op flatten container
24 ::peg::peg::op minimize container
26 ::peg::peg::op modeopt container
28 ::peg::peg::op reachable container
30 ::peg::peg::op realizable container
32______________________________________________________________________________
34
36 Are you lost ? Do you have trouble understanding this document ? In
37 that case please read the overview provided by the Introduction to
38 Parser Tools. This document is the entrypoint to the whole system the
39 current package is a part of.
40 This package provides a number of utility commands manipulating a PE
42 grammar (container) in various ways.
43
45 ::peg::peg::op called container
46 This command determines the static call structure for the non‐
47 terminal symbols of the grammar stored in the container.
48 The result of the command is a dictionary mapping from each sym‐
50 bol to the symbols it calls. The empty string is the key used to
51 represent the start expression of the grammar.
52 The grammar in the container is not modified.
54 The container instance has to expose a method API as is provided
56 by the package pt::peg::container.
57 ::peg::peg::op dechain container
59 This command simplifies all symbols which just chain to a dif‐
60 ferent symbol by inlining the right hand side of the called sym‐
61 bol in its callers. This works if and only the modes match prop‐
62 erly, per the decision table below.
63 caller called | dechain | notes
67 --------------+---------+-----------------------
68 value value | yes | value is passed
69 value leaf | yes | value is passed
70 value void | yes | caller is implied void
71 leaf value | no | generated value was discarded, inlined would not. called may be implied void.
72 leaf leaf | no | s.a.
73 leaf void | no | s.a.
74 void value | no | caller drops value, inlined would not.
75 void leaf | no | s.a.
76 void void | yes |
77 The result of the command is the empty string.
80 The grammar in the container is directly modified. If that is not
82 wanted, a copy of the original container has to be used.
83 The container instance has to expose a method API as is provided by the
85 package pt::peg::container.
86 ::peg::peg::op drop unreachable container
88 This command removes all symbols from the grammar which are not
89 reachable.
90 The result of the command is the empty string.
92 The grammar in the container is directly modified. If that is
94 not wanted, a copy of the original container has to be used.
95 The container instance has to expose a method API as is provided
97 by the package pt::peg::container.
98 ::peg::peg::op drop unrealizable container
100 This command removes all symbols from the grammar which are not
101 realizable.
102 The result of the command is the empty string.
104 The grammar in the container is directly modified. If that is
106 not wanted, a copy of the original container has to be used.
107 The container instance has to expose a method API as is provided
109 by the package pt::peg::container.
110 ::peg::peg::op flatten container
112 This command flattens (see pt::pe::op) all expressions in the
113 grammar, i.e. the start expression and the right hand sides of
114 all nonterminal symbols.
115 The result of the command is the empty string.
117 The grammar in the container is directly modified. If that is
119 not wanted, a copy of the original container has to be used.
120 The container instance has to expose a method API as is provided
122 by the package pt::peg::container.
123 ::peg::peg::op minimize container
125 This command reduces the provided grammar by applying most of
126 the other methods of this package.
127 After flattening the expressions it removes unreachable and un‐
129 realizable symbols, flattens the expressions again, then opti‐
130 mizes the symbol modes before collapsing symbol chains as much
131 as possible.
132 The result of the command is the empty string.
134 The grammar in the container is directly modified. If that is
136 not wanted, a copy of the original container has to be used.
137 The container instance has to expose a method API as is provided
139 by the package pt::peg::container.
140 ::peg::peg::op modeopt container
142 This command optimizes the semantic modes of non-terminal sym‐
143 bols according to the two rules below.
144 [1] If a symbol X with mode value calls no other symbols,
146 i.e. uses only terminal symbols in whatever combination,
147 then this can be represented simpler by using mode leaf.
148 [2] If a symbol X is only called from symbols with modes leaf
150 or void then this symbol should have mode void also, as
151 any AST it could generate will be discarded anyway.
152 The result of the command is the empty string.
154 The grammar in the container is directly modified. If that is not
156 wanted, a copy of the original container has to be used.
157 The container instance has to expose a method API as is provided by the
159 package pt::peg::container.
160 ::peg::peg::op reachable container
162 This command computes the set of all nonterminal symbols which
163 are reachable from the start expression of the grammar. This is
164 essentially the transitive closure over called and the symbol's
165 right hand sides, beginning with the start expression.
166 The result of the command is the list of reachable symbols.
168 The grammar in the container is not modified.
170 The container instance has to expose a method API as is provided
172 by the package pt::peg::container.
173 ::peg::peg::op realizable container
175 This command computes the set of all nonterminal symbols which
176 are realizable, i.e. can derive pure terminal phrases. This is
177 done iteratively, starting with state unrealizable for all and
178 any, and then updating all symbols which are realizable, propa‐
179 gating changes, until nothing changes any more.
180 The result of the command is the list of realizable symbols.
182 The grammar in the container is not modified.
184 The container instance has to expose a method API as is provided
186 by the package pt::peg::container.
187
189 This document, and the package it describes, will undoubtedly contain
190 bugs and other problems. Please report such in the category pt of the
191 Tcllib Trackers [http://core.tcl.tk/tcllib/reportlist]. Please also
192 report any ideas for enhancements you may have for either package
193 and/or documentation.
194 When proposing code changes, please provide unified diffs, i.e the out‐
196 put of diff -u.
197 Note further that attachments are strongly preferred over inlined
199 patches. Attachments can be made by going to the Edit form of the
200 ticket immediately after its creation, and then using the left-most
201 button in the secondary navigation bar.
202
204 EBNF, LL(k), PEG, TDPL, context-free languages, expression, grammar,
205 matching, parser, parsing expression, parsing expression grammar, push
206 down automaton, recursive descent, state, top-down parsing languages,
207 transducer
208
210 Parsing and Grammars
211
213 Copyright (c) 2009 Andreas Kupries <andreas_kupries@users.sourceforge.net>
214tcllib 1.1.0 pt_peg_op(i)