Commit 75a08d51 authored by POTTIER Francois's avatar POTTIER Francois

Introduce [accepting_state_can_have_successors].

parent 8fa7e1f1
......@@ -392,6 +392,18 @@ type dfa = {
expressions. Then, we construct a DFA whose states are the reachable
expressions and whose transitions correspond to derivation. *)
(* If one wishes to stop as soon as an accepting state is encountered, then a
final state need not have any outgoing transitions; that would be
pointless. However, in some applications, one might wish to record that an
accepting state was reached and nevertheless continue reading the input. In
that case, the following flag should be set to true]. *)
let accepting_state_can_have_successors =
false
let may_have_successors (e : regexp) : bool =
accepting_state_can_have_successors || not (nullable e)
let dfa (e : regexp) : dfa =
(* Discover and number the nonempty reachable expressions. The most
nontrivial aspect of this phase is termination. The fact that expressions
......@@ -401,14 +413,15 @@ let dfa (e : regexp) : dfa =
more expressions being identified, therefore smaller automata. *)
let module G = struct
type t = regexp
(* The successors of [e] are its derivatives along every character [a],
provided they are nonempty. *)
let foreach_successor e f =
Char.foreach (fun a ->
let e' = delta a e in
if nonempty e' then
f e'
)
if may_have_successors e then
(* The successors of [e] are its derivatives along every character
[a], provided they are nonempty. *)
Char.foreach (fun a ->
let e' = delta a e in
if nonempty e' then
f e'
)
(* The single root is [e], if it is nonempty. *)
let foreach_root f =
if nonempty e then
......@@ -425,7 +438,12 @@ let dfa (e : regexp) : dfa =
(* The initial state is the encoding of [e]. *)
let init = encode e in
(* The transition function is as follows. *)
let transition q a = encode (delta a (decode q)) in
let transition q a =
if may_have_successors (decode q) then
encode (delta a (decode q))
else
None
in
(* We are done. *)
{ n; init; decode; transition }
......
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