(* Author: Tobias Nipkow *)
section \<open>Unbalanced Tree Implementation of Map\<close>
theory Tree_Map
imports
Tree_Set
Map_by_Ordered
begin
fun lookup :: "('a::linorder*'b) tree \<Rightarrow> 'a \<Rightarrow> 'b option" where
"lookup Leaf x = None" |
"lookup (Node l (a,b) r) x =
(case cmp x a of LT \<Rightarrow> lookup l x | GT \<Rightarrow> lookup r x | EQ \<Rightarrow> Some b)"
fun update :: "'a::linorder \<Rightarrow> 'b \<Rightarrow> ('a*'b) tree \<Rightarrow> ('a*'b) tree" where
"update x y Leaf = Node Leaf (x,y) Leaf" |
"update x y (Node l (a,b) r) = (case cmp x a of
LT \<Rightarrow> Node (update x y l) (a,b) r |
EQ \<Rightarrow> Node l (x,y) r |
GT \<Rightarrow> Node l (a,b) (update x y r))"
fun delete :: "'a::linorder \<Rightarrow> ('a*'b) tree \<Rightarrow> ('a*'b) tree" where
"delete x Leaf = Leaf" |
"delete x (Node l (a,b) r) = (case cmp x a of
LT \<Rightarrow> Node (delete x l) (a,b) r |
GT \<Rightarrow> Node l (a,b) (delete x r) |
EQ \<Rightarrow> if r = Leaf then l else let (ab',r') = del_min r in Node l ab' r')"
subsection "Functional Correctness Proofs"
lemma lookup_map_of:
"sorted1(inorder t) \<Longrightarrow> lookup t x = map_of (inorder t) x"
by (induction t) (auto simp: map_of_simps split: option.split)
lemma inorder_update:
"sorted1(inorder t) \<Longrightarrow> inorder(update a b t) = upd_list a b (inorder t)"
by(induction t) (auto simp: upd_list_simps)
lemma inorder_delete:
"sorted1(inorder t) \<Longrightarrow> inorder(delete x t) = del_list x (inorder t)"
by(induction t) (auto simp: del_list_simps del_minD split: prod.splits)
interpretation Map_by_Ordered
where empty = Leaf and lookup = lookup and update = update and delete = delete
and inorder = inorder and inv = "\<lambda>_. True"
proof (standard, goal_cases)
case 1 show ?case by simp
next
case 2 thus ?case by(simp add: lookup_map_of)
next
case 3 thus ?case by(simp add: inorder_update)
next
case 4 thus ?case by(simp add: inorder_delete)
qed auto
end