@[export my_function]
def my_function (s: String): String :=
  s ++ s!" at callee"

  -- Formats a string in 3 different forms
@[export stylize]
def stylize (s: String): (String × String × String) :=
  (s.capitalize, s.decapitalize, s.toUpper)

inductive Think where
  | Success (s: String)
  | Failure (i: Nat)

@[export think]
def think (s: String): Think :=
  if s.front == 'S' then
    Think.Success (s.drop 1)
  else
    Think.Failure s.length