Commit 7662ce58 authored by POTTIER Francois's avatar POTTIER Francois
Browse files

More cleanup.

parent 68b4af50
......@@ -371,53 +371,103 @@ let answer : question -> =
let es = ref 0
let backward (s', z) : =
let module G = struct
type vertex = Lr1.node * Terminal.t
(* A vertex is a pair [s, z]. *)
type vertex =
Lr1.node * Terminal.t
let equal (s'1, z1) (s'2, z2) = s'1 s'2 = 0 && z1 z2 = 0
let hash (s, z) = Hashtbl.hash (Lr1.number s, z)
type label = int * Terminal.t Seq.seq
let weight (w, _) = w
let hash (s, z) =
Hashtbl.hash (Lr1.number s, z)
(* An edge is labeled with a property of the form [Finite (i, pi)],
that is, a distance [i] and a witness path [pi]. *)
type label =
int * Terminal.t Seq.seq
let weight (w, _) =
(* Backward search from the single source [s', z]. *)
let sources f = f (s', z)
let successors edge (s', z) =
match Lr1.incoming_symbol s' with
| None ->
(* A start symbol has no predecessors. *)
(* An entry state has no predecessor states. *)
| Some (Symbol.T t) ->
List.iter (fun pred ->
edge (1, Seq.singleton t) (pred, t)
(* There is an edge from [s] to [s'] labeled [t] in the automaton.
Thus, our graph has an edge from [s', z] to [s, t], labeled [t]. *)
let label = (1, Seq.singleton t) in
List.iter (fun s ->
edge label (s, t)
) (Lr1.predecessors s')
| Some (Symbol.N nt) ->
List.iter (fun pred ->
(* There is an edge from [s] to [s'] labeled [nt] in the automaton.
For every production [prod] associated with [nt], for every
letter [a], we query the analysis for a path that begins in [s]
and leads to reducing [prod] when the lookahead symbol is [z].
Such a path [w] takes us from [s, a] to [s', z]. Thus, our graph
has an edge, labeled [w], in the reverse direction. *)
List.iter (fun s ->
Production.foldnt nt () (fun prod () ->
TerminalSet.iter (fun a ->
match answer { s = pred; a = a; prod = prod; i = 0; z = z } with
match answer { s = s; a = a; prod = prod; i = 0; z = z } with
| P.Infinity ->
| P.Finite (w, ts) ->
edge (w, ts) (pred, a)
edge (w, ts) (s, a)
) (first prod 0 z)
) (Lr1.predecessors s')
end in
let module D = Dijkstra.Make(G) in
let module S = struct exception Success of end in
(* Search backwards from [s', z], stopping as soon as an entry state
is reached. In that case, return the distance [i] and path [pi]
that have been found. *)
let _ = (fun (distance, (v', _), path) ->
let _ = (fun (i, (s, _), labels) ->
(* Debugging. TEMPORARY *)
incr es;
if !es mod 10000 = 0 then
Printf.fprintf stderr "es = %d\n%!" !es;
if Lr1.incoming_symbol v' = None then
let path = snd path in
raise (S.Success (P.Finite (distance, Seq.concat path))) (* TEMPORARY keep path *)
(* If [s] is a start state... *)
if Lr1.incoming_symbol s = None then
(* [labels] is a list of graph labels. Projecting onto the second
component yields a list of paths (sequences of terminal symbols),
which we concatenate to obtain a path. Because the edges that were
followed last are in front of the list, and because this is a
reverse graph, we obtain a path that makes direct sense: it is a
sequence of terminal symbols that will take the automaton into
state [s'] if the next (unconsumed) symbol is [z]. *)
let path = P.Finite (i, Seq.concat ( snd labels)) in
raise (S.Success path)
) in
with S.Success p ->
(* ------------------------------------------------------------------------ *)
(* For each state [s'] and for each terminal symbol [z] such that [z] triggers
an error in [s'], backward search is performed. For each state [s'], we
stop as soon as one [z] is found, i.e., as soon as one way of causing an
error in state [s'] is found. *)
let backward s' : =
(* Debugging. TEMPORARY *)
Printf.fprintf stderr
"Attempting to reach an error in state %d:\n%!"
(Lr1.number s');
......@@ -429,7 +479,7 @@ let backward s' : =
(* Test. *)
(* Test. TEMPORARY *)
let () =
Lr1.iter (fun s' ->
Markdown is supported
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment