doc-src/Codegen/Thy/examples/pick1.ML

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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 m (Suc n) = less_eq_nat m n
  | less_nat n Zero_nat = false
and less_eq_nat (Suc m) n = less_nat m n
  | less_eq_nat Zero_nat n = 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 f (a, b) = f 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*)