structure HOL = 

 struct

 fun leta s f = f s;

 end; (*struct HOL*)

 structure Nat = 

 struct

 datatype nat = Suc of nat | Zero_nat;

 fun less_nat n (Suc m) = less_eq_nat n m

   | less_nat n Zero_nat = false

 and less_eq_nat (Suc n) m = less_nat n m

   | less_eq_nat Zero_nat m = true;

 fun minus_nat (Suc m) (Suc n) = minus_nat m n

   | minus_nat Zero_nat n = Zero_nat

   | minus_nat m Zero_nat = m;

 end; (*struct Nat*)

 structure Product_Type = 

 struct

 fun split c (a, b) = c a b;

 end; (*struct Product_Type*)

 structure Codegen = 

 struct

 fun pick ((k, v) :: xs) n =

   (if Nat.less_nat n k then v else pick xs (Nat.minus_nat n k))

   | pick (x :: xs) n =

     let

       val a = x;

       val (k, v) = a;

     in

       (if Nat.less_nat n k then v else pick xs (Nat.minus_nat n k))

     end;

 end; (*struct Codegen*)