Quelle  Value.thy

(*  Title:      HOL/Bali/Value.thy
    Author:     David von Oheimb
*)
subsection ‹Java values›



theory Value imports Type begin

typedecl loc            ― ‹locations, i.e. abstract references on objects›

datatype val
        = Unit          ― ‹dummy result value of void methods›
        | Bool bool     ― ‹Boolean value›
        | Intg int      ― ‹integer value›
        | Null          ― ‹null reference›
        | Addr loc      ― ‹addresses, i.e. locations of objects›


primrec the_Bool :: "val → bool"
  where "the_Bool (Bool b) = b"

primrec the_Intg :: "val → int"
  where "the_Intg (Intg i) = i"

primrec the_Addr :: "val → loc"
  where "the_Addr (Addr a) = a"

type_synonym dyn_ty = "loc → ty option"

primrec typeof :: "dyn_ty → val → ty option"
where
  "typeof dt Unit = Some (PrimT Void)"
| "typeof dt (Bool b) = Some (PrimT Boolean)"
| "typeof dt (Intg i) = Some (PrimT Integer)"
| "typeof dt Null = Some NT"
| "typeof dt (Addr a) = dt a"

primrec defpval :: "prim_ty → val"  ― ‹default value for primitive types›
where
  "defpval Void = Unit"
| "defpval Boolean = Bool False"
| "defpval Integer = Intg 0"

primrec default_val :: "ty → val"  ― ‹default value for all types›
where
  "default_val (PrimT pt) = defpval pt"
| "default_val (RefT r ) = Null"

end