moved recursion combinator to HOL/Library/Wfrec.thy -- it is so fundamental and well-known that it should survive recdef
structure HOL =
struct
datatype boola = False | True;
fun anda x True = x
| anda x False = False
| anda True x = x
| anda False x = False;
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 = HOL.False
and less_eq_nat (Suc m) n = less_nat m n
| less_eq_nat Zero_nat n = HOL.True;
end; (*struct Nat*)
structure Codegen =
struct
fun in_interval (k, l) n =
HOL.anda (Nat.less_eq_nat k n) (Nat.less_eq_nat n l);
end; (*struct Codegen*)