lean4-htt/tests/lean/repr_issue.lean

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def foo {m} [Monad m] [MonadExcept String m] [MonadState (Array Nat) m] : m Nat :=
catch (do modify $ fun (a : Array Nat) => a.set! 0 33;
throw "error")
(fun _ => do a ← get; pure $ a.get! 0)
def ex₁ : StateT (Array Nat) (ExceptT String Id) Nat :=
foo
def ex₂ : ExceptT String (StateT (Array Nat) Id) Nat :=
foo
-- The following examples were producing an element of Type `id (Except String Nat)`.
-- Type class resolution was failing to produce an instance for `HasRepr (id (Except String Nat))` because `id` is not transparent.
#eval run ex₁ (mkArray 10 1000)
#eval run ex₂ (mkArray 10 1000)