1 | (* *********************************************************************) |
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2 | (* *) |
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3 | (* The Compcert verified compiler *) |
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4 | (* *) |
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5 | (* Xavier Leroy, INRIA Paris-Rocquencourt *) |
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6 | (* *) |
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7 | (* Copyright Institut National de Recherche en Informatique et en *) |
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8 | (* Automatique. All rights reserved. This file is distributed *) |
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9 | (* under the terms of the GNU General Public License as published by *) |
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10 | (* the Free Software Foundation, either version 2 of the License, or *) |
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11 | (* (at your option) any later version. This file is also distributed *) |
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12 | (* under the terms of the INRIA Non-Commercial License Agreement. *) |
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13 | (* *) |
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14 | (* *********************************************************************) |
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15 | |
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16 | include "basics/types.ma". |
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17 | include "basics/logic.ma". |
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18 | include "basics/list.ma". |
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19 | include "common/PreIdentifiers.ma". |
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20 | |
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21 | (* * Error reporting and the error monad. *) |
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22 | |
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23 | (* * * Representation of error messages. *) |
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24 | |
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25 | (* * Compile-time errors produce an error message, represented in Coq |
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26 | as a list of either substrings or positive numbers encoding |
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27 | a source-level identifier (see module AST). *) |
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28 | |
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29 | inductive errcode: Type[0] := |
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30 | | MSG: String → errcode |
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31 | | CTX: ∀tag:String. identifier tag → errcode. |
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32 | |
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33 | definition errmsg: Type[0] ≝ list errcode. |
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34 | |
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35 | definition msg : String → errmsg ≝ λs. [MSG s]. |
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36 | |
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37 | (* * * The error monad *) |
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38 | |
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39 | (* * Compilation functions that can fail have return type [res A]. |
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40 | The return value is either [OK res] to indicate success, |
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41 | or [Error msg] to indicate failure. *) |
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42 | |
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43 | inductive res (A: Type[0]) : Type[0] ≝ |
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44 | | OK: A → res A |
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45 | | Error: errmsg → res A. |
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46 | |
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47 | (*Implicit Arguments Error [A].*) |
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48 | |
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49 | (* * To automate the propagation of errors, we use a monadic style |
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50 | with the following [bind] operation. *) |
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51 | |
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52 | definition bind ≝ λA,B:Type[0]. λf: res A. λg: A → res B. |
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53 | match f with |
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54 | [ OK x ⇒ g x |
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55 | | Error msg ⇒ Error ? msg |
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56 | ]. |
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57 | |
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58 | definition bind2 ≝ λA,B,C: Type[0]. λf: res (A × B). λg: A → B → res C. |
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59 | match f with |
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60 | [ OK v ⇒ match v with [ pair x y ⇒ g x y ] |
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61 | | Error msg => Error ? msg |
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62 | ]. |
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63 | |
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64 | definition bind3 ≝ λA,B,C,D: Type[0]. λf: res (A × B × C). λg: A → B → C → res D. |
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65 | match f with |
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66 | [ OK v ⇒ match v with [ pair xy z ⇒ match xy with [ pair x y ⇒ g x y z ] ] |
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67 | | Error msg => Error ? msg |
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68 | ]. |
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69 | |
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70 | (* Not sure what level to use *) |
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71 | notation > "vbox('do' ident v ← e; break e')" with precedence 40 for @{'bind ${e} (λ${ident v}.${e'})}. |
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72 | notation > "vbox('do' ident v : ty ← e; break e')" with precedence 40 for @{'bind ${e} (λ${ident v} : ${ty}.${e'})}. |
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73 | notation < "vbox('do' \nbsp ident v ← e; break e')" with precedence 40 for @{'bind ${e} (λ${ident v}.${e'})}. |
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74 | notation < "vbox('do' \nbsp ident v : ty ← e; break e')" with precedence 40 for @{'bind ${e} (λ${ident v} : ${ty}.${e'})}. |
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75 | interpretation "error monad bind" 'bind e f = (bind ?? e f). |
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76 | notation > "vbox('do' 〈ident v1, ident v2〉 ← e; break e')" with precedence 40 for @{'bind2 ${e} (λ${ident v1}.λ${ident v2}.${e'})}. |
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77 | notation > "vbox('do' 〈ident v1 : ty1, ident v2 : ty2〉 ← e; break e')" with precedence 40 for @{'bind2 ${e} (λ${ident v1} : ${ty1}.λ${ident v2} : ${ty2}.${e'})}. |
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78 | notation < "vbox('do' \nbsp 〈ident v1, ident v2〉 ← e; break e')" with precedence 40 for @{'bind2 ${e} (λ${ident v1}.λ${ident v2}.${e'})}. |
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79 | notation < "vbox('do' \nbsp 〈ident v1 : ty1, ident v2 : ty2〉 ← e; break e')" with precedence 40 for @{'bind2 ${e} (λ${ident v1} : ${ty1}.λ${ident v2} : ${ty2}.${e'})}. |
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80 | interpretation "error monad Prod bind" 'bind2 e f = (bind2 ??? e f). |
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81 | notation > "vbox('do' 〈ident v1, ident v2, ident v3〉 ← e; break e')" with precedence 40 for @{'bind3 ${e} (λ${ident v1}.λ${ident v2}.λ${ident v3}.${e'})}. |
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82 | notation > "vbox('do' 〈ident v1 : ty1, ident v2 : ty2, ident v3 : ty3〉 ← e; break e')" with precedence 40 for @{'bind3 ${e} (λ${ident v1} : ${ty1}.λ${ident v2} : ${ty2}.λ${ident v3} : ${ty3}.${e'})}. |
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83 | notation < "vbox('do' \nbsp 〈ident v1, ident v2, ident v3〉 ← e; break e')" with precedence 40 for @{'bind3 ${e} (λ${ident v1}.λ${ident v2}.λ${ident v3}.${e'})}. |
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84 | notation < "vbox('do' \nbsp 〈ident v1 : ty1, ident v2 : ty2, ident v3 : ty3〉 ← e; break e')" with precedence 40 for @{'bind3 ${e} (λ${ident v1} : ${ty1}.λ${ident v2} : ${ty2}.λ${ident v3} : ${ty3}.${e'})}. |
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85 | interpretation "error monad triple bind" 'bind3 e f = (bind3 ???? e f). |
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86 | (*interpretation "error monad ret" 'ret e = (ret ? e). |
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87 | notation "'ret' e" non associative with precedence 45 for @{'ret ${e}}.*) |
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88 | |
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89 | (* |
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90 | (** The [do] notation, inspired by Haskell's, keeps the code readable. *) |
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91 | |
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92 | Notation "'do' X <- A ; B" := (bind A (fun X => B)) |
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93 | (at level 200, X ident, A at level 100, B at level 200) |
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94 | : error_monad_scope. |
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95 | |
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96 | Notation "'do' ( X , Y ) <- A ; B" := (bind2 A (fun X Y => B)) |
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97 | (at level 200, X ident, Y ident, A at level 100, B at level 200) |
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98 | : error_monad_scope. |
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99 | *) |
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100 | lemma bind_inversion: |
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101 | ∀A,B: Type[0]. ∀f: res A. ∀g: A → res B. ∀y: B. |
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102 | bind ?? f g = OK ? y → |
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103 | ∃x. f = OK ? x ∧ g x = OK ? y. |
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104 | #A #B #f #g #y cases f; |
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105 | [ #a #e %{a} whd in e:(??%?); /2/; |
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106 | | #m #H whd in H:(??%?); destruct (H); |
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107 | ] qed. |
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108 | |
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109 | lemma bind2_inversion: |
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110 | ∀A,B,C: Type[0]. ∀f: res (A×B). ∀g: A → B → res C. ∀z: C. |
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111 | bind2 ??? f g = OK ? z → |
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112 | ∃x. ∃y. f = OK ? 〈x, y〉 ∧ g x y = OK ? z. |
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113 | #A #B #C #f #g #z cases f; |
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114 | [ #ab cases ab; #a #b #e %{a} %{b} whd in e:(??%?); /2/; |
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115 | | #m #H whd in H:(??%?); destruct |
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116 | ] qed. |
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117 | |
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118 | (* |
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119 | Open Local Scope error_monad_scope. |
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120 | |
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121 | (** This is the familiar monadic map iterator. *) |
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122 | *) |
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123 | |
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124 | let rec mmap (A, B: Type[0]) (f: A → res B) (l: list A) on l : res (list B) ≝ |
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125 | match l with |
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126 | [ nil ⇒ OK ? [] |
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127 | | cons hd tl ⇒ do hd' ← f hd; do tl' ← mmap ?? f tl; OK ? (hd'::tl') |
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128 | ]. |
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129 | |
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130 | (* |
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131 | lemma mmap_inversion: |
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132 | ∀A, B: Type[0]. ∀f: A -> res B. ∀l: list A. ∀l': list B. |
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133 | mmap A B f l = OK ? l' → |
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134 | list_forall2 (fun x y => f x = OK y) l l'. |
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135 | Proof. |
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136 | induction l; simpl; intros. |
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137 | inversion_clear H. constructor. |
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138 | destruct (bind_inversion _ _ H) as [hd' [P Q]]. |
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139 | destruct (bind_inversion _ _ Q) as [tl' [R S]]. |
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140 | inversion_clear S. |
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141 | constructor. auto. auto. |
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142 | Qed. |
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143 | *) |
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144 | |
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145 | (* A monadic fold_left2 *) |
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146 | |
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147 | axiom WrongLength: String. |
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148 | |
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149 | let rec mfold_left2 |
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150 | (A: Type[0]) (B: Type[0]) (C: Type[0]) (f: A → B → C → res A) (accu: res A) |
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151 | (left: list B) (right: list C) on left: res A ≝ |
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152 | match left with |
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153 | [ nil ⇒ |
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154 | match right with |
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155 | [ nil ⇒ accu |
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156 | | cons hd tl ⇒ Error ? (msg WrongLength) |
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157 | ] |
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158 | | cons hd tl ⇒ |
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159 | match right with |
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160 | [ nil ⇒ Error ? (msg WrongLength) |
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161 | | cons hd' tl' ⇒ |
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162 | do accu ← accu; |
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163 | mfold_left2 … f (f accu hd hd') tl tl' |
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164 | ] |
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165 | ]. |
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166 | |
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167 | (* |
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168 | (** * Reasoning over monadic computations *) |
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169 | |
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170 | (** The [monadInv H] tactic below simplifies hypotheses of the form |
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171 | << |
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172 | H: (do x <- a; b) = OK res |
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173 | >> |
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174 | By definition of the bind operation, both computations [a] and |
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175 | [b] must succeed for their composition to succeed. The tactic |
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176 | therefore generates the following hypotheses: |
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177 | |
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178 | x: ... |
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179 | H1: a = OK x |
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180 | H2: b x = OK res |
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181 | *) |
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182 | |
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183 | Ltac monadInv1 H := |
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184 | match type of H with |
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185 | | (OK _ = OK _) => |
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186 | inversion H; clear H; try subst |
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187 | | (Error _ = OK _) => |
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188 | discriminate |
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189 | | (bind ?F ?G = OK ?X) => |
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190 | let x := fresh "x" in ( |
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191 | let EQ1 := fresh "EQ" in ( |
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192 | let EQ2 := fresh "EQ" in ( |
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193 | destruct (bind_inversion F G H) as [x [EQ1 EQ2]]; |
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194 | clear H; |
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195 | try (monadInv1 EQ2)))) |
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196 | | (bind2 ?F ?G = OK ?X) => |
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197 | let x1 := fresh "x" in ( |
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198 | let x2 := fresh "x" in ( |
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199 | let EQ1 := fresh "EQ" in ( |
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200 | let EQ2 := fresh "EQ" in ( |
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201 | destruct (bind2_inversion F G H) as [x1 [x2 [EQ1 EQ2]]]; |
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202 | clear H; |
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203 | try (monadInv1 EQ2))))) |
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204 | | (mmap ?F ?L = OK ?M) => |
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205 | generalize (mmap_inversion F L H); intro |
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206 | end. |
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207 | |
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208 | Ltac monadInv H := |
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209 | match type of H with |
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210 | | (OK _ = OK _) => monadInv1 H |
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211 | | (Error _ = OK _) => monadInv1 H |
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212 | | (bind ?F ?G = OK ?X) => monadInv1 H |
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213 | | (bind2 ?F ?G = OK ?X) => monadInv1 H |
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214 | | (?F _ _ _ _ _ _ _ _ = OK _) => |
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215 | ((progress simpl in H) || unfold F in H); monadInv1 H |
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216 | | (?F _ _ _ _ _ _ _ = OK _) => |
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217 | ((progress simpl in H) || unfold F in H); monadInv1 H |
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218 | | (?F _ _ _ _ _ _ = OK _) => |
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219 | ((progress simpl in H) || unfold F in H); monadInv1 H |
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220 | | (?F _ _ _ _ _ = OK _) => |
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221 | ((progress simpl in H) || unfold F in H); monadInv1 H |
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222 | | (?F _ _ _ _ = OK _) => |
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223 | ((progress simpl in H) || unfold F in H); monadInv1 H |
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224 | | (?F _ _ _ = OK _) => |
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225 | ((progress simpl in H) || unfold F in H); monadInv1 H |
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226 | | (?F _ _ = OK _) => |
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227 | ((progress simpl in H) || unfold F in H); monadInv1 H |
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228 | | (?F _ = OK _) => |
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229 | ((progress simpl in H) || unfold F in H); monadInv1 H |
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230 | end. |
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231 | *) |
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232 | |
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233 | |
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234 | definition opt_to_res ≝ λA.λmsg.λv:option A. match v with [ None ⇒ Error A msg | Some v ⇒ OK A v ]. |
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235 | lemma opt_OK: ∀A,m,P,e. |
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236 | (∀v. e = Some ? v → P v) → |
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237 | match opt_to_res A m e with [ Error _ ⇒ True | OK v ⇒ P v ]. |
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238 | #A #m #P #e elim e; /2/; |
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239 | qed. |
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