src/HOL/Library/Code_Target_Int.thy
 author haftmann Wed Jan 01 11:35:21 2014 +0100 (2014-01-01) changeset 54891 2f4491f15fe6 parent 54796 cdc6d8cbf770 child 55736 f1ed1e9cd080 permissions -rw-r--r--
examples how to avoid the "code, code del" antipattern
```     1 (*  Title:      HOL/Library/Code_Target_Int.thy
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```     2     Author:     Florian Haftmann, TU Muenchen
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```     3 *)
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```     4
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```     5 header {* Implementation of integer numbers by target-language integers *}
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```     6
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```     7 theory Code_Target_Int
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```     8 imports Main
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```     9 begin
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```    10
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```    11 code_datatype int_of_integer
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```    12
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```    13 declare [[code drop: integer_of_int]]
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```    14
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```    15 lemma [code]:
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```    16   "integer_of_int (int_of_integer k) = k"
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```    17   by transfer rule
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```    18
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```    19 lemma [code]:
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```    20   "Int.Pos = int_of_integer \<circ> integer_of_num"
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```    21   by transfer (simp add: fun_eq_iff)
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```    22
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```    23 lemma [code]:
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```    24   "Int.Neg = int_of_integer \<circ> uminus \<circ> integer_of_num"
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```    25   by transfer (simp add: fun_eq_iff)
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```    26
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```    27 lemma [code_abbrev]:
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```    28   "int_of_integer (numeral k) = Int.Pos k"
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```    29   by transfer simp
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```    30
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```    31 lemma [code_abbrev]:
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```    32   "int_of_integer (- numeral k) = Int.Neg k"
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```    33   by transfer simp
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```    34
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```    35 lemma [code, symmetric, code_post]:
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```    36   "0 = int_of_integer 0"
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```    37   by transfer simp
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```    38
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```    39 lemma [code, symmetric, code_post]:
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```    40   "1 = int_of_integer 1"
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```    41   by transfer simp
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```    42
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```    43 lemma [code]:
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```    44   "k + l = int_of_integer (of_int k + of_int l)"
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```    45   by transfer simp
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```    46
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```    47 lemma [code]:
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```    48   "- k = int_of_integer (- of_int k)"
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```    49   by transfer simp
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```    50
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```    51 lemma [code]:
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```    52   "k - l = int_of_integer (of_int k - of_int l)"
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```    53   by transfer simp
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```    54
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```    55 lemma [code]:
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```    56   "Int.dup k = int_of_integer (Code_Numeral.dup (of_int k))"
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```    57   by transfer simp
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```    58
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```    59 declare [[code drop: Int.sub]]
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```    60
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```    61 lemma [code]:
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```    62   "k * l = int_of_integer (of_int k * of_int l)"
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```    63   by simp
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```    64
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```    65 lemma [code]:
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```    66   "Divides.divmod_abs k l = map_pair int_of_integer int_of_integer
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```    67     (Code_Numeral.divmod_abs (of_int k) (of_int l))"
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```    68   by (simp add: prod_eq_iff)
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```    69
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```    70 lemma [code]:
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```    71   "k div l = int_of_integer (of_int k div of_int l)"
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```    72   by simp
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```    73
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```    74 lemma [code]:
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```    75   "k mod l = int_of_integer (of_int k mod of_int l)"
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```    76   by simp
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```    77
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```    78 lemma [code]:
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```    79   "HOL.equal k l = HOL.equal (of_int k :: integer) (of_int l)"
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```    80   by transfer (simp add: equal)
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```    81
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```    82 lemma [code]:
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```    83   "k \<le> l \<longleftrightarrow> (of_int k :: integer) \<le> of_int l"
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```    84   by transfer rule
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```    85
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```    86 lemma [code]:
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```    87   "k < l \<longleftrightarrow> (of_int k :: integer) < of_int l"
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```    88   by transfer rule
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```    89
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```    90 lemma (in ring_1) of_int_code_if:
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```    91   "of_int k = (if k = 0 then 0
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```    92      else if k < 0 then - of_int (- k)
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```    93      else let
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```    94        (l, j) = divmod_int k 2;
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```    95        l' = 2 * of_int l
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```    96      in if j = 0 then l' else l' + 1)"
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```    97 proof -
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```    98   from mod_div_equality have *: "of_int k = of_int (k div 2 * 2 + k mod 2)" by simp
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```    99   show ?thesis
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```   100     by (simp add: Let_def divmod_int_mod_div of_int_add [symmetric])
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```   101       (simp add: * mult_commute)
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```   102 qed
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```   103
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```   104 declare of_int_code_if [code]
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```   105
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```   106 lemma [code]:
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```   107   "nat = nat_of_integer \<circ> of_int"
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```   108   by transfer (simp add: fun_eq_iff)
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```   109
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```   110 code_identifier
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```   111   code_module Code_Target_Int \<rightharpoonup>
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```   112     (SML) Arith and (OCaml) Arith and (Haskell) Arith
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```   113
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```   114 end
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```   115
```