An example scaml code to fail `tezos-client typecheck script`

typeerror.ml

open SCaml

type parameter = nat * unit contract * unit

type storage = nat

let main (param: parameter) (storage: storage) =
  let (counter, contr, sigs) = param in
  (*  let counter = counter in *) (* If this line is available then the typecheck will be passed. *)
  if counter <> Nat 1 then failwith "0" else
    let op = Operation.transfer_tokens () (Tz 1.) contr in
    ([op], counter)

The iml by scaml --dump-iml typeerror.ml.

(fun global_param_1163 ->
   (fun storage_1162 ->
      (let __v_1175
         = (global_param_1163 </* = __x_1170 *//* = __param_1184 *//* = param_1153 *//* = __v_1185 *//* = __param_1164 */> : pair nat (pair (contract unit) unit))
       in
       (let __r_1176
          = (snd (__v_1175 : pair nat (pair (contract unit) unit)) : pair (contract unit) unit)
        in
        ((let __counter_1172
            = (fst (__v_1175 : pair nat (pair (contract unit) unit)) </* = counter_1155 *//* = __l_1177 */> : nat)
          in
          (fun __contr_1173 ->
             (fun __sigs_1174 ->
                (if (<> (__counter_1172 : nat) (1 : nat) : bool)
                 then (failwith ("0" : string) : pair (list operation) nat)
                 else (((Operation.transfer_tokens (() : unit) (1000000 : mutez) (__contr_1173 : contract unit) </* = __op_1168 *//* = op_1158 *//* = __v_1169 *//* = __x_1166 */> : operation) :: ([] : list operation) : list operation),
                       (__counter_1172 : nat) : pair (list operation) nat) : pair (list operation) nat) : lambda unit (pair (list operation) nat)) : lambda (contract unit) (lambda unit (pair (list operation) nat))) : lambda (contract unit) (lambda unit (pair (list operation) nat))) 
        (fst (__r_1176 : pair (contract unit) unit) </* = contr_1156 *//* = __l_1179 */> : contract unit) (snd (__r_1176 : pair (contract unit) unit) </* = sigs_1157 *//* = __r_1178 */> : unit) : pair (list operation) nat) : pair (list operation) nat) </* entry main_1152 */> : pair (list operation) nat) : lambda nat (pair (list operation) nat)) : lambda (pair nat (pair (contract unit) unit)) (lambda nat (pair (list operation) nat)))