data Exp = Const Int | Reg Int | Plus Exp Exp | Times Exp Exp

data Instr = LoadImm Int | LoadReg Int | AddInstr | MulInstr

match select (e : Exp) : Instr =
  | Plus (Reg a) (Reg b) -> AddInstr
  | Times (Reg a) (Reg b) -> MulInstr
  | Const n -> LoadImm n
  | Reg n -> LoadReg n
  | _ -> LoadImm 0