(* Title: HOL/Library/Ref.thy
ID: $Id$
Author: John Matthews, Galois Connections; Alexander Krauss, Lukas Bulwahn & Florian Haftmann, TU Muenchen
*)
header {* Monadic references *}
theory Ref
imports Heap_Monad
begin
text {*
Imperative reference operations; modeled after their ML counterparts.
See http://caml.inria.fr/pub/docs/manual-caml-light/node14.15.html
and http://www.smlnj.org/doc/Conversion/top-level-comparison.html
*}
subsection {* Primitives *}
definition
new :: "'a\<Colon>heap \<Rightarrow> 'a ref Heap" where
[code del]: "new v = Heap_Monad.heap (Heap.ref v)"
definition
lookup :: "'a\<Colon>heap ref \<Rightarrow> 'a Heap" ("!_" 61) where
[code del]: "lookup r = Heap_Monad.heap (\<lambda>h. (get_ref r h, h))"
definition
update :: "'a ref \<Rightarrow> ('a\<Colon>heap) \<Rightarrow> unit Heap" ("_ := _" 62) where
[code del]: "update r e = Heap_Monad.heap (\<lambda>h. ((), set_ref r e h))"
subsection {* Derivates *}
definition
change :: "('a\<Colon>heap \<Rightarrow> 'a) \<Rightarrow> 'a ref \<Rightarrow> 'a Heap"
where
"change f r = (do x \<leftarrow> ! r;
let y = f x;
r := y;
return y
done)"
hide (open) const new lookup update change
subsection {* Properties *}
lemma lookup_chain:
"(!r \<guillemotright> f) = f"
by (cases f)
(auto simp add: Let_def bindM_def lookup_def expand_fun_eq)
lemma update_change [code]:
"r := e = Ref.change (\<lambda>_. e) r \<guillemotright> return ()"
by (auto simp add: monad_simp change_def lookup_chain)
subsection {* Code generator setup *}
subsubsection {* SML *}
code_type ref (SML "_/ ref")
code_const Ref (SML "raise/ (Fail/ \"bare Ref\")")
code_const Ref.new (SML "(fn/ ()/ =>/ ref/ _)")
code_const Ref.lookup (SML "(fn/ ()/ =>/ !/ _)")
code_const Ref.update (SML "(fn/ ()/ =>/ _/ :=/ _)")
code_reserved SML ref
subsubsection {* OCaml *}
code_type ref (OCaml "_/ ref")
code_const Ref (OCaml "failwith/ \"bare Ref\")")
code_const Ref.new (OCaml "(fn/ ()/ =>/ ref/ _)")
code_const Ref.lookup (OCaml "(fn/ ()/ =>/ !/ _)")
code_const Ref.update (OCaml "(fn/ ()/ =>/ _/ :=/ _)")
code_reserved OCaml ref
subsubsection {* Haskell *}
code_type ref (Haskell "Heap.STRef/ Heap.RealWorld/ _")
code_const Ref (Haskell "error/ \"bare Ref\"")
code_const Ref.new (Haskell "Heap.newSTRef")
code_const Ref.lookup (Haskell "Heap.readSTRef")
code_const Ref.update (Haskell "Heap.writeSTRef")
end