Commit 59bffe97 authored by POTTIER Francois's avatar POTTIER Francois
Browse files

Updated [Invariant] with the constraint that an end position must exist on top...

Updated [Invariant] with the constraint that an end position must exist on top of the stack whenever an epsilon production is about to be reduced.
parent deb1fad5
......@@ -595,6 +595,17 @@ let rewind node : instruction =
rewind w
(* ------------------------------------------------------------------------ *)
(* This auxiliary function tests whether a state has a reduction action for
an epsilon production. It could be moved to [Lr1], if desired. *)
let has_epsilon_reduction node =
TerminalMap.fold (fun _ prods accu ->
accu ||
let prod = Misc.single prods in
Production.length prod = 0
) (Lr1.reductions node) false
(* ------------------------------------------------------------------------ *)
(* We now determine which positions must be kept track of. For
simplicity, we do this on a per symbol basis. That is, for each
......@@ -613,6 +624,14 @@ let rewind node : instruction =
(resp. last) symbol of its right-hand side (if there is one) must
do so as well. That is, unless the right-hand side is empty. *)
(* 2015/11/04. When an epsilon production is reduced, the top stack cell is
consulted for its end position. This implies that this cell must exist and
must store an end position! Thus, we have the following constraint: if some
state whose incoming symbol is [sym] can reduce an epsilon production, then
[sym] must keep track of its end position. (Furthermore, if some initial
state can reduce an epsilon production, then the sentinel cell at the bottom
of the stack must contain a position. This does not concern us here.) *)
open Keyword
let startp =
......@@ -665,6 +684,12 @@ let () =
require where rhs.(i)
) ids
) (Action.keywords action)
Lr1.iterx (fun node ->
(* 2015/11/04. See above. *)
if has_epsilon_reduction node then
let sym = Misc.unSome (Lr1.incoming_symbol node) in
require WhereEnd sym
let startp =
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