New function [Lr0.compare].

src/lr0.ml

@@ -363,6 +363,20 @@ let equal ((k1, toksr1) as state1) ((k2, toksr2) as state2) =
   in
   loop (Array.length toksr1)
 
+(* A total order on states. *)
+
+let compare ((k1, toksr1) as state1) ((k2, toksr2) as state2) =
+  assert (k1 = k2 && well_formed state1 && well_formed state2);
+  let rec loop i =
+    if i = 0 then
+      0
+    else
+      let i = i - 1 in
+      let c = TerminalSet.compare toksr1.(i) toksr2.(i) in
+      if c <> 0 then c else loop i
+  in
+  loop (Array.length toksr1)
+
 (* Subsumption between states. *)
 
 let subsume ((k1, toksr1) as state1) ((k2, toksr2) as state2) =

src/lr0.mli

@@ -88,6 +88,12 @@ val reductions: lr1state -> (TerminalSet.t * Production.index) list
 
 val equal: lr1state -> lr1state -> bool
 
+(* A total order on states. The two states must have the same core.
+   This is an arbitrary total order; it has nothing to do with set
+   inclusion, which is a partial order; see [subsume] below. *)
+
+val compare: lr1state -> lr1state -> int
+
 (* Subsumption between states. The two states must have the same
    core. Then, one subsumes the other if and only if their lookahead
    sets are (pointwise) in the subset relation. *)
@@ -128,4 +134,3 @@ val restrict: TerminalSet.t -> lr1state -> lr1state
 val print_concrete: string -> concretelr1state -> string
 val print:          string ->         lr1state -> string
 val print_closure:  string ->         lr1state -> string
-