minor improvement of an error message

src/core/pretty.ml

@@ -506,8 +506,9 @@ let () = Exn_printer.register
   | Ty.BadTypeArity ({ts_args = []} as ts, _) ->
       fprintf fmt "Type symbol %a expects no arguments" print_ts ts
   | Ty.BadTypeArity (ts, app_arg) ->
-      fprintf fmt "Type symbol %a expects %i arguments but is applied to %i"
-        print_ts ts (List.length ts.ts_args) app_arg
+      let i = List.length ts.ts_args in
+      fprintf fmt "Type symbol %a expects %i argument%s but is applied to %i"
+        print_ts ts i (if i = 1 then "" else "s") app_arg
   | Ty.DuplicateTypeVar tv ->
       fprintf fmt "Type variable %a is used twice" print_tv tv
   | Ty.UnboundTypeVar tv ->
@@ -518,9 +519,10 @@ let () = Exn_printer.register
       fprintf fmt "%s %a expects no arguments"
         (if ls.ls_value = None then "Predicate" else "Function") print_ls ls
   | Term.BadArity (ls, app_arg) ->
-      fprintf fmt "%s %a expects %i arguments but is applied to %i"
+      let i = List.length ls.ls_args in
+      fprintf fmt "%s %a expects %i argument%s but is applied to %i"
         (if ls.ls_value = None then "Predicate" else "Function")
-        print_ls ls (List.length ls.ls_args) app_arg
+        print_ls ls i (if i = 1 then "" else "s") app_arg
   | Term.EmptyCase ->
       fprintf fmt "Empty match expression"
   | Term.DuplicateVar vs ->

src/core/theory.ml

@@ -907,10 +907,11 @@ let () = Exn_printer.register
       Format.fprintf fmt "Metaproperty %s is already registered with \
         a conflicting signature" m.meta_name
   | BadMetaArity (m,n) ->
-      Format.fprintf fmt "Metaproperty %s requires %d arguments but \
-        is applied to %d" m.meta_name (List.length m.meta_type) n
+      let i = List.length m.meta_type in
+      Format.fprintf fmt "Metaproperty %s expects %d argument%s but \
+        is applied to %d" m.meta_name i (if i = 1 then "" else "s") n
   | MetaTypeMismatch (m,t1,t2) ->
-      Format.fprintf fmt "Metaproperty %s expects %a argument but \
+      Format.fprintf fmt "Metaproperty %s expects a %a argument but \
         is applied to %a"
         m.meta_name print_meta_arg_type t1 print_meta_arg_type t2
   | _ -> raise exn

src/whyml/mlw_pretty.ml

@@ -432,12 +432,14 @@ let () = Exn_printer.register
   | Mlw_ty.BadItyArity ({its_ts = {ts_args = []}} as ts, _) ->
       fprintf fmt "Type symbol %a expects no arguments" print_its ts
   | Mlw_ty.BadItyArity (ts, app_arg) ->
-      fprintf fmt "Type symbol %a expects %i arguments but is applied to %i"
-        print_its ts (List.length ts.its_ts.ts_args) app_arg
+      let i = List.length ts.its_ts.ts_args in
+      fprintf fmt "Type symbol %a expects %i argument%s but is applied to %i"
+        print_its ts i (if i = 1 then "" else "s") app_arg
   | Mlw_ty.BadRegArity (ts, app_arg) ->
+      let i = List.length ts.its_regs in
       fprintf fmt "Type symbol %a expects \
-                   %i region arguments but is applied to %i"
-        print_its ts (List.length ts.its_regs) app_arg
+                   %i region argument%s but is applied to %i"
+        print_its ts i (if i = 1 then "" else "s") app_arg
   | Mlw_ty.DuplicateRegion r ->
       fprintf fmt "Region %a is used twice" print_reg r
   | Mlw_ty.UnboundRegion r ->