src/HOL/Option.thy
 author nipkow Fri Mar 06 17:38:47 2009 +0100 (2009-03-06) changeset 30313 b2441b0c8d38 parent 30246 8253519dfc90 child 30327 4d1185c77f4a permissions -rw-r--r--
```     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 option_caseE:
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```    24   assumes c: "(case x of None => P | Some y => Q y)"
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```    25   obtains
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```    26     (None) "x = None" and P
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```    27   | (Some) y where "x = Some y" and "Q y"
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```    28   using c by (cases x) simp_all
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```    29
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```    30 lemma insert_None_conv_UNIV: "insert None (range Some) = UNIV"
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```    31   by (rule set_ext, case_tac x) auto
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```    32
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```    33 lemma inj_Some [simp]: "inj_on Some A"
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```    34   by (rule inj_onI) simp
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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
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```    60   map :: "('a \<Rightarrow> 'b) \<Rightarrow> 'a option \<Rightarrow> 'b option"
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```    61 where
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```    62   [code del]: "map = (%f y. case y of None => None | Some x => Some (f x))"
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```    63
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```    64 lemma option_map_None [simp, code]: "map f None = None"
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```    65   by (simp add: map_def)
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```    66
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```    67 lemma option_map_Some [simp, code]: "map f (Some x) = Some (f x)"
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```    68   by (simp add: map_def)
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```    69
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```    70 lemma option_map_is_None [iff]:
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```    71     "(map f opt = None) = (opt = None)"
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```    72   by (simp add: map_def split add: option.split)
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```    73
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```    74 lemma option_map_eq_Some [iff]:
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```    75     "(map f xo = Some y) = (EX z. xo = Some z & f z = y)"
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```    76   by (simp add: map_def split add: option.split)
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```    77
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```    78 lemma option_map_comp:
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```    79     "map f (map g opt) = map (f o g) opt"
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```    80   by (simp add: map_def split add: option.split)
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```    81
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```    82 lemma option_map_o_sum_case [simp]:
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```    83     "map f o sum_case g h = sum_case (map f o g) (map f o h)"
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```    84   by (rule ext) (simp split: sum.split)
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```    85
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```    86
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```    87 hide (open) const set map
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```    88
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```    89 subsubsection {* Code generator setup *}
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```    90
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```    91 definition
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```    92   is_none :: "'a option \<Rightarrow> bool" where
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```    93   is_none_none [code post, symmetric, code inline]: "is_none x \<longleftrightarrow> x = None"
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```    94
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```    95 lemma is_none_code [code]:
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```    96   shows "is_none None \<longleftrightarrow> True"
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```    97     and "is_none (Some x) \<longleftrightarrow> False"
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```    98   unfolding is_none_none [symmetric] by simp_all
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```    99
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```   100 hide (open) const is_none
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```   101
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```   102 code_type option
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```   103   (SML "_ option")
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```   104   (OCaml "_ option")
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```   105   (Haskell "Maybe _")
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```   106
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```   107 code_const None and Some
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```   108   (SML "NONE" and "SOME")
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```   109   (OCaml "None" and "Some _")
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```   110   (Haskell "Nothing" and "Just")
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```   111
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```   112 code_instance option :: eq
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```   113   (Haskell -)
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```   114
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```   115 code_const "eq_class.eq \<Colon> 'a\<Colon>eq option \<Rightarrow> 'a option \<Rightarrow> bool"
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```   116   (Haskell infixl 4 "==")
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```   117
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```   118 code_reserved SML
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```   119   option NONE SOME
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```   120
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```   121 code_reserved OCaml
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```   122   option None Some
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```   123
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```   124 end
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