separate initializations for different modes of partial_function -- generation of induction rules will be non-uniform
(* Title: HOL/Option.thy
Author: Folklore
*)
header {* Datatype option *}
theory Option
imports Datatype
begin
datatype 'a option = None | Some 'a
lemma not_None_eq [iff]: "(x ~= None) = (EX y. x = Some y)"
by (induct x) auto
lemma not_Some_eq [iff]: "(ALL y. x ~= Some y) = (x = None)"
by (induct x) auto
text{*Although it may appear that both of these equalities are helpful
only when applied to assumptions, in practice it seems better to give
them the uniform iff attribute. *}
lemma inj_Some [simp]: "inj_on Some A"
by (rule inj_onI) simp
lemma option_caseE:
assumes c: "(case x of None => P | Some y => Q y)"
obtains
(None) "x = None" and P
| (Some) y where "x = Some y" and "Q y"
using c by (cases x) simp_all
lemma UNIV_option_conv: "UNIV = insert None (range Some)"
by(auto intro: classical)
subsubsection {* Operations *}
primrec the :: "'a option => 'a" where
"the (Some x) = x"
primrec set :: "'a option => 'a set" where
"set None = {}" |
"set (Some x) = {x}"
lemma ospec [dest]: "(ALL x:set A. P x) ==> A = Some x ==> P x"
by simp
declaration {* fn _ =>
Classical.map_cs (fn cs => cs addSD2 ("ospec", @{thm ospec}))
*}
lemma elem_set [iff]: "(x : set xo) = (xo = Some x)"
by (cases xo) auto
lemma set_empty_eq [simp]: "(set xo = {}) = (xo = None)"
by (cases xo) auto
definition map :: "('a \<Rightarrow> 'b) \<Rightarrow> 'a option \<Rightarrow> 'b option" where
"map = (%f y. case y of None => None | Some x => Some (f x))"
lemma option_map_None [simp, code]: "map f None = None"
by (simp add: map_def)
lemma option_map_Some [simp, code]: "map f (Some x) = Some (f x)"
by (simp add: map_def)
lemma option_map_is_None [iff]:
"(map f opt = None) = (opt = None)"
by (simp add: map_def split add: option.split)
lemma option_map_eq_Some [iff]:
"(map f xo = Some y) = (EX z. xo = Some z & f z = y)"
by (simp add: map_def split add: option.split)
lemma option_map_comp:
"map f (map g opt) = map (f o g) opt"
by (simp add: map_def split add: option.split)
lemma option_map_o_sum_case [simp]:
"map f o sum_case g h = sum_case (map f o g) (map f o h)"
by (rule ext) (simp split: sum.split)
enriched_type map: Option.map proof -
fix f g
show "Option.map f \<circ> Option.map g = Option.map (f \<circ> g)"
proof
fix x
show "(Option.map f \<circ> Option.map g) x= Option.map (f \<circ> g) x"
by (cases x) simp_all
qed
next
show "Option.map id = id"
proof
fix x
show "Option.map id x = id x"
by (cases x) simp_all
qed
qed
primrec bind :: "'a option \<Rightarrow> ('a \<Rightarrow> 'b option) \<Rightarrow> 'b option" where
bind_lzero: "bind None f = None" |
bind_lunit: "bind (Some x) f = f x"
lemma bind_runit[simp]: "bind x Some = x"
by (cases x) auto
lemma bind_assoc[simp]: "bind (bind x f) g = bind x (\<lambda>y. bind (f y) g)"
by (cases x) auto
lemma bind_rzero[simp]: "bind x (\<lambda>x. None) = None"
by (cases x) auto
hide_const (open) set map bind
subsubsection {* Code generator setup *}
definition is_none :: "'a option \<Rightarrow> bool" where
[code_post]: "is_none x \<longleftrightarrow> x = None"
lemma is_none_code [code]:
shows "is_none None \<longleftrightarrow> True"
and "is_none (Some x) \<longleftrightarrow> False"
unfolding is_none_def by simp_all
lemma [code_unfold]:
"HOL.equal x None \<longleftrightarrow> is_none x"
by (simp add: equal is_none_def)
hide_const (open) is_none
code_type option
(SML "_ option")
(OCaml "_ option")
(Haskell "Maybe _")
(Scala "!Option[(_)]")
code_const None and Some
(SML "NONE" and "SOME")
(OCaml "None" and "Some _")
(Haskell "Nothing" and "Just")
(Scala "!None" and "Some")
code_instance option :: equal
(Haskell -)
code_const "HOL.equal \<Colon> 'a option \<Rightarrow> 'a option \<Rightarrow> bool"
(Haskell infix 4 "==")
code_reserved SML
option NONE SOME
code_reserved OCaml
option None Some
code_reserved Scala
Option None Some
end