(* Title: HOL/Tools/Function/sum_tree.ML
Author: Alexander Krauss, TU Muenchen
Some common tools for working with sum types in balanced tree form.
*)
structure SumTree =
struct
(* Theory dependencies *)
val proj_in_rules = [@{thm "Datatype.Projl_Inl"}, @{thm "Datatype.Projr_Inr"}]
val sumcase_split_ss = HOL_basic_ss addsimps (@{thm "Product_Type.split"} :: @{thms "sum.cases"})
(* top-down access in balanced tree *)
fun access_top_down {left, right, init} len i =
Balanced_Tree.access {left = (fn f => f o left), right = (fn f => f o right), init = I} len i init
(* Sum types *)
fun mk_sumT LT RT = Type ("+", [LT, RT])
fun mk_sumcase TL TR T l r = Const (@{const_name sum.sum_case}, (TL --> T) --> (TR --> T) --> mk_sumT TL TR --> T) $ l $ r
val App = curry op $
fun mk_inj ST n i =
access_top_down
{ init = (ST, I : term -> term),
left = (fn (T as Type ("+", [LT, RT]), inj) => (LT, inj o App (Const (@{const_name Inl}, LT --> T)))),
right =(fn (T as Type ("+", [LT, RT]), inj) => (RT, inj o App (Const (@{const_name Inr}, RT --> T))))} n i
|> snd
fun mk_proj ST n i =
access_top_down
{ init = (ST, I : term -> term),
left = (fn (T as Type ("+", [LT, RT]), proj) => (LT, App (Const (@{const_name Datatype.Projl}, T --> LT)) o proj)),
right =(fn (T as Type ("+", [LT, RT]), proj) => (RT, App (Const (@{const_name Datatype.Projr}, T --> RT)) o proj))} n i
|> snd
fun mk_sumcases T fs =
Balanced_Tree.make (fn ((f, fT), (g, gT)) => (mk_sumcase fT gT T f g, mk_sumT fT gT))
(map (fn f => (f, domain_type (fastype_of f))) fs)
|> fst
end