4 files changed, 18 insertions, 9 deletions
diff --git a/kernel/inductive.ml b/kernel/inductive.ml
index d7181299e1..c9399925bb 100644
--- a/kernel/inductive.ml
+++ b/kernel/inductive.ml
@@ -222,14 +222,13 @@ let is_info_arity env c =
 
 let error_elim_expln env kp ki =
   if is_info_arity env kp && not (is_info_arity env ki) then
-    "non-informative objects may not construct informative ones."
+    NonInformativeToInformative
   else 
     match (kind_of_term kp,kind_of_term ki) with 
-      | Sort (Type _), Sort (Prop _) ->
-          "strong elimination on non-small inductive types leads to paradoxes."
-      | _ -> "wrong arity"
+      | Sort (Type _), Sort (Prop _) -> StrongEliminationOnNonSmallType
+      | _ -> WrongArity
 
-exception Arity of (constr * constr * string) option
+exception Arity of (constr * constr * arity_error) option
 
 
 let is_correct_arity env kelim (c,pj) indf t = 
diff --git a/kernel/inductive.mli b/kernel/inductive.mli
index 7e08a31c00..720ae3e4a7 100644
--- a/kernel/inductive.mli
+++ b/kernel/inductive.mli
@@ -46,7 +46,7 @@ val type_of_constructor  : env -> constructor -> types
 val arities_of_constructors : env -> inductive -> types array
 
 
-exception Arity of (constr * constr * string) option
+exception Arity of (constr * constr * Type_errors.arity_error) option
 
 (* [type_case_branches env (I,args) (p:A) c] computes useful types
    about the following Cases expression:
diff --git a/kernel/type_errors.ml b/kernel/type_errors.ml
index f1eb32b5bc..fc98a2ef16 100644
--- a/kernel/type_errors.ml
+++ b/kernel/type_errors.ml
@@ -34,6 +34,11 @@ type guard_error =
   | RecCallInCasePred of constr
   | NotGuardedForm
 
+type arity_error =
+  | NonInformativeToInformative
+  | StrongEliminationOnNonSmallType
+  | WrongArity
+
 type type_error =
   | UnboundRel of int
   | UnboundVar of variable
@@ -41,7 +46,7 @@ type type_error =
   | BadAssumption of unsafe_judgment
   | ReferenceVariables of constr
   | ElimArity of inductive * types list * constr * unsafe_judgment
-      * (constr * constr * string) option
+      * (constr * constr * arity_error) option
   | CaseNotInductive of unsafe_judgment
   | WrongCaseInfo of inductive * case_info
   | NumberBranches of unsafe_judgment * int
diff --git a/kernel/type_errors.mli b/kernel/type_errors.mli
index 99b46877a8..a18ffd7e53 100644
--- a/kernel/type_errors.mli
+++ b/kernel/type_errors.mli
@@ -36,6 +36,11 @@ type guard_error =
   | RecCallInCasePred of constr
   | NotGuardedForm
 
+type arity_error =
+  | NonInformativeToInformative
+  | StrongEliminationOnNonSmallType
+  | WrongArity
+
 type type_error =
   | UnboundRel of int
   | UnboundVar of variable
@@ -43,7 +48,7 @@ type type_error =
   | BadAssumption of unsafe_judgment
   | ReferenceVariables of constr
   | ElimArity of inductive * types list * constr * unsafe_judgment
-      * (constr * constr * string) option
+      * (constr * constr * arity_error) option
   | CaseNotInductive of unsafe_judgment
   | WrongCaseInfo of inductive * case_info
   | NumberBranches of unsafe_judgment * int
@@ -71,7 +76,7 @@ val error_reference_variables : env -> constr -> 'a
 
 val error_elim_arity : 
   env -> inductive -> types list -> constr 
-    -> unsafe_judgment -> (constr * constr * string) option -> 'a
+    -> unsafe_judgment -> (constr * constr * arity_error) option -> 'a
 
 val error_case_not_inductive : env -> unsafe_judgment -> 'a