A last example

• datatype expr = INT of int
  | UNARY of string * expr
  | BINARY of string * expr * expr

• fun print(INT n) = Int.toString(n)
  | print(UNARY(s, e)) =
  ``('' ^ s ^ print(e) ^ ``)''
  | print(BINARY(s, e1, e2)) =
  ``('' ^ print(e1) ^ s ^
  print(e2) ^ ``)''

• print(BINARY(``*'', INT 5, BINARY(``+''
  UNARY(``-'', INT 3), INT 4)))

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