abbrev M := ExceptT String $ ExceptT Nat $ StateM Nat

def inc (x : Nat) : M Unit := do
if (← get) >= 100 then
  throwThe Nat ((← get) + x)
modify (· + x)

def dec (x : Nat) : M Unit := do
if (← get) - x == 0 then
  throw "balance is zero"
modify (· - x)

def f (x y : Nat) : M Nat := do
try
  inc x
  dec y
  get
catch ex : String =>
  dbg_trace "string exception {ex}"
  pure 1000
catch ex : Nat =>
  dbg_trace "nat exception {ex}"
  pure ex

/--
info: nat exception 1010
---
info: (Except.ok (Except.ok 1010), 1000)
-/
#guard_msgs in
#eval (f 10 20).run 1000

/--
info: string exception balance is zero
---
info: (Except.ok (Except.ok 1000), 20)
-/
#guard_msgs in
#eval (f 10 200).run 10

/-- info: (Except.ok (Except.ok 20), 20) -/
#guard_msgs in
#eval (f 10 20).run 30