+ | ["value", "coercion"] -> Obj_class (`Coercion 0)
+ | ("value", "coercion")::["arity",n]
+ | ("arity",n)::["value", "coercion"] ->
+ let arity = try int_of_string n with Failure _ ->
+ parse_error "\"arity\" must be an integer"
+ in
+ Obj_class (`Coercion arity)