src/HOL/Option.thy
 author hoelzl Tue Jan 18 21:37:23 2011 +0100 (2011-01-18) changeset 41654 32fe42892983 parent 41505 6d19301074cf child 46526 c4cf9d03c352 permissions -rw-r--r--
Gauge measure removed
```     1 (*  Title:      HOL/Option.thy
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```     2     Author:     Folklore
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```     3 *)
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```     4
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```     5 header {* Datatype option *}
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```     6
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```     7 theory Option
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```     8 imports Datatype
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```     9 begin
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```    10
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```    11 datatype 'a option = None | Some 'a
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```    12
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```    13 lemma not_None_eq [iff]: "(x ~= None) = (EX y. x = Some y)"
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```    14   by (induct x) auto
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```    15
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```    16 lemma not_Some_eq [iff]: "(ALL y. x ~= Some y) = (x = None)"
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```    17   by (induct x) auto
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```    18
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```    19 text{*Although it may appear that both of these equalities are helpful
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```    20 only when applied to assumptions, in practice it seems better to give
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```    21 them the uniform iff attribute. *}
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```    22
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```    23 lemma inj_Some [simp]: "inj_on Some A"
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```    24 by (rule inj_onI) simp
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```    25
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```    26 lemma option_caseE:
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```    27   assumes c: "(case x of None => P | Some y => Q y)"
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```    28   obtains
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```    29     (None) "x = None" and P
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```    30   | (Some) y where "x = Some y" and "Q y"
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```    31   using c by (cases x) simp_all
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```    32
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```    33 lemma UNIV_option_conv: "UNIV = insert None (range Some)"
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```    34 by(auto intro: classical)
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```    35
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```    36
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```    37 subsubsection {* Operations *}
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```    38
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```    39 primrec the :: "'a option => 'a" where
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```    40 "the (Some x) = x"
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```    41
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```    42 primrec set :: "'a option => 'a set" where
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```    43 "set None = {}" |
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```    44 "set (Some x) = {x}"
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```    45
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```    46 lemma ospec [dest]: "(ALL x:set A. P x) ==> A = Some x ==> P x"
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```    47   by simp
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```    48
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```    49 declaration {* fn _ =>
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```    50   Classical.map_cs (fn cs => cs addSD2 ("ospec", @{thm ospec}))
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```    51 *}
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```    52
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```    53 lemma elem_set [iff]: "(x : set xo) = (xo = Some x)"
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```    54   by (cases xo) auto
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```    55
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```    56 lemma set_empty_eq [simp]: "(set xo = {}) = (xo = None)"
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```    57   by (cases xo) auto
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```    58
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```    59 definition map :: "('a \<Rightarrow> 'b) \<Rightarrow> 'a option \<Rightarrow> 'b option" where
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```    60   "map = (%f y. case y of None => None | Some x => Some (f x))"
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```    61
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```    62 lemma option_map_None [simp, code]: "map f None = None"
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```    63   by (simp add: map_def)
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```    64
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```    65 lemma option_map_Some [simp, code]: "map f (Some x) = Some (f x)"
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```    66   by (simp add: map_def)
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```    67
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```    68 lemma option_map_is_None [iff]:
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```    69     "(map f opt = None) = (opt = None)"
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```    70   by (simp add: map_def split add: option.split)
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```    71
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```    72 lemma option_map_eq_Some [iff]:
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```    73     "(map f xo = Some y) = (EX z. xo = Some z & f z = y)"
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```    74   by (simp add: map_def split add: option.split)
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```    75
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```    76 lemma option_map_comp:
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```    77     "map f (map g opt) = map (f o g) opt"
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```    78   by (simp add: map_def split add: option.split)
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```    79
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```    80 lemma option_map_o_sum_case [simp]:
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```    81     "map f o sum_case g h = sum_case (map f o g) (map f o h)"
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```    82   by (rule ext) (simp split: sum.split)
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```    83
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```    84 enriched_type map: Option.map proof -
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```    85   fix f g
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```    86   show "Option.map f \<circ> Option.map g = Option.map (f \<circ> g)"
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```    87   proof
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```    88     fix x
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```    89     show "(Option.map f \<circ> Option.map g) x= Option.map (f \<circ> g) x"
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```    90       by (cases x) simp_all
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```    91   qed
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```    92 next
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```    93   show "Option.map id = id"
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```    94   proof
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```    95     fix x
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```    96     show "Option.map id x = id x"
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```    97       by (cases x) simp_all
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```    98   qed
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```    99 qed
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```   100
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```   101 primrec bind :: "'a option \<Rightarrow> ('a \<Rightarrow> 'b option) \<Rightarrow> 'b option" where
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```   102 bind_lzero: "bind None f = None" |
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```   103 bind_lunit: "bind (Some x) f = f x"
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```   104
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```   105 lemma bind_runit[simp]: "bind x Some = x"
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```   106 by (cases x) auto
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```   107
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```   108 lemma bind_assoc[simp]: "bind (bind x f) g = bind x (\<lambda>y. bind (f y) g)"
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```   109 by (cases x) auto
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```   110
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```   111 lemma bind_rzero[simp]: "bind x (\<lambda>x. None) = None"
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```   112 by (cases x) auto
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```   113
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```   114 hide_const (open) set map bind
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```   115
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```   116 subsubsection {* Code generator setup *}
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```   117
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```   118 definition is_none :: "'a option \<Rightarrow> bool" where
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```   119   [code_post]: "is_none x \<longleftrightarrow> x = None"
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```   120
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```   121 lemma is_none_code [code]:
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```   122   shows "is_none None \<longleftrightarrow> True"
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```   123     and "is_none (Some x) \<longleftrightarrow> False"
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```   124   unfolding is_none_def by simp_all
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```   125
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```   126 lemma [code_unfold]:
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```   127   "HOL.equal x None \<longleftrightarrow> is_none x"
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```   128   by (simp add: equal is_none_def)
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```   129
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```   130 hide_const (open) is_none
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```   131
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```   132 code_type option
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```   133   (SML "_ option")
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```   134   (OCaml "_ option")
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```   135   (Haskell "Maybe _")
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```   136   (Scala "!Option[(_)]")
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```   137
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```   138 code_const None and Some
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```   139   (SML "NONE" and "SOME")
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```   140   (OCaml "None" and "Some _")
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```   141   (Haskell "Nothing" and "Just")
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```   142   (Scala "!None" and "Some")
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```   143
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```   144 code_instance option :: equal
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```   145   (Haskell -)
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```   146
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```   147 code_const "HOL.equal \<Colon> 'a option \<Rightarrow> 'a option \<Rightarrow> bool"
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```   148   (Haskell infix 4 "==")
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```   149
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```   150 code_reserved SML
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```   151   option NONE SOME
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```   152
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```   153 code_reserved OCaml
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```   154   option None Some
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```   155
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```   156 code_reserved Scala
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```   157   Option None Some
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```   158
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```   159 end
```