structure ROOT =
struct
structure IntDef =
struct
datatype nat = Zero_nat | Succ_nat of nat;
fun less_nat Zero_nat (Succ_nat n) = true
| less_nat n Zero_nat = false
| less_nat (Succ_nat m) (Succ_nat n) = less_nat m n;
fun minus_nat (Succ_nat m) (Succ_nat n) = minus_nat m n
| minus_nat Zero_nat n = Zero_nat
| minus_nat y Zero_nat = y;
end; (*struct IntDef*)
structure Codegen =
struct
fun pick ((k, v) :: xs) n =
(if IntDef.less_nat n k then v else pick xs (IntDef.minus_nat n k))
| pick (x :: xs) n =
let
val (ka, va) = x;
in
(if IntDef.less_nat n ka then va else pick xs (IntDef.minus_nat n ka))
end;
end; (*struct Codegen*)
end; (*struct ROOT*)