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Progress and preservation
author Adam Chlipala <adamc@hcoop.net>
date Sun, 02 Nov 2008 13:14:08 -0500
parents 8c19768f1a1a
children b31ca896f211
rev   line source
adamc@152 1 (* Copyright (c) 2008, Adam Chlipala
adamc@152 2 *
adamc@152 3 * This work is licensed under a
adamc@152 4 * Creative Commons Attribution-Noncommercial-No Derivative Works 3.0
adamc@152 5 * Unported License.
adamc@152 6 * The license text is available at:
adamc@152 7 * http://creativecommons.org/licenses/by-nc-nd/3.0/
adamc@152 8 *)
adamc@152 9
adamc@152 10 (* begin hide *)
adamc@152 11 Require Import List String.
adamc@152 12
adamc@152 13 Require Import Tactics.
adamc@152 14
adamc@152 15 Set Implicit Arguments.
adamc@152 16 (* end hide *)
adamc@152 17
adamc@152 18
adamc@153 19 (** %\part{Formalizing Programming Languages and Compilers}
adamc@152 20
adamc@153 21 \chapter{First-Order Abstract Syntax}% *)
adamc@152 22
adamc@152 23 (** TODO: Prose for this chapter *)
adamc@152 24
adamc@152 25
adamc@152 26 (** * Concrete Binding *)
adamc@152 27
adamc@152 28 Module Concrete.
adamc@152 29
adamc@152 30 Definition var := string.
adamc@152 31 Definition var_eq := string_dec.
adamc@152 32
adamc@152 33 Inductive exp : Set :=
adamc@152 34 | Const : bool -> exp
adamc@152 35 | Var : var -> exp
adamc@152 36 | App : exp -> exp -> exp
adamc@152 37 | Abs : var -> exp -> exp.
adamc@152 38
adamc@152 39 Inductive type : Set :=
adamc@152 40 | Bool : type
adamc@152 41 | Arrow : type -> type -> type.
adamc@152 42
adamc@152 43 Infix "-->" := Arrow (right associativity, at level 60).
adamc@152 44
adamc@152 45 Definition ctx := list (var * type).
adamc@152 46
adamc@152 47 Reserved Notation "G |-v x : t" (no associativity, at level 90, x at next level).
adamc@152 48
adamc@152 49 Inductive lookup : ctx -> var -> type -> Prop :=
adamc@152 50 | First : forall x t G,
adamc@152 51 (x, t) :: G |-v x : t
adamc@152 52 | Next : forall x t x' t' G,
adamc@152 53 x <> x'
adamc@152 54 -> G |-v x : t
adamc@152 55 -> (x', t') :: G |-v x : t
adamc@152 56
adamc@152 57 where "G |-v x : t" := (lookup G x t).
adamc@152 58
adamc@152 59 Hint Constructors lookup.
adamc@152 60
adamc@152 61 Reserved Notation "G |-e e : t" (no associativity, at level 90, e at next level).
adamc@152 62
adamc@152 63 Inductive hasType : ctx -> exp -> type -> Prop :=
adamc@152 64 | TConst : forall G b,
adamc@152 65 G |-e Const b : Bool
adamc@152 66 | TVar : forall G v t,
adamc@152 67 G |-v v : t
adamc@152 68 -> G |-e Var v : t
adamc@152 69 | TApp : forall G e1 e2 dom ran,
adamc@152 70 G |-e e1 : dom --> ran
adamc@152 71 -> G |-e e2 : dom
adamc@152 72 -> G |-e App e1 e2 : ran
adamc@152 73 | TAbs : forall G x e' dom ran,
adamc@152 74 (x, dom) :: G |-e e' : ran
adamc@152 75 -> G |-e Abs x e' : dom --> ran
adamc@152 76
adamc@152 77 where "G |-e e : t" := (hasType G e t).
adamc@152 78
adamc@152 79 Hint Constructors hasType.
adamc@152 80
adamc@152 81 Notation "x ## G" := (forall t' : type, In (x, t') G -> False) (no associativity, at level 90).
adamc@152 82
adamc@152 83 Notation "G' # G" := (forall (x : var) (t : type), In (x, t) G -> x ## G') (no associativity, at level 90).
adamc@152 84
adamc@152 85 Lemma lookup_In : forall G x t,
adamc@152 86 G |-v x : t
adamc@152 87 -> In (x, t) G.
adamc@152 88 induction 1; crush.
adamc@152 89 Qed.
adamc@152 90
adamc@152 91 Hint Resolve lookup_In.
adamc@152 92
adamc@152 93 Lemma disjoint_invert1 : forall G x t G' x' t',
adamc@152 94 G |-v x : t
adamc@152 95 -> (x', t') :: G' # G
adamc@152 96 -> x <> x'.
adamc@152 97 crush; eauto.
adamc@152 98 Qed.
adamc@152 99
adamc@152 100 Lemma disjoint_invert2 : forall G' G p,
adamc@152 101 p :: G' # G
adamc@152 102 -> G' # G.
adamc@152 103 firstorder.
adamc@152 104 Qed.
adamc@152 105
adamc@152 106 Hint Resolve disjoint_invert1 disjoint_invert2.
adamc@152 107 Hint Extern 1 (_ <> _) => (intro; subst).
adamc@152 108
adamc@152 109 Lemma weaken_lookup' : forall G x t,
adamc@152 110 G |-v x : t
adamc@152 111 -> forall G', G' # G
adamc@152 112 -> G' ++ G |-v x : t.
adamc@152 113 induction G' as [ | [x' t'] tl ]; crush; eauto 9.
adamc@152 114 Qed.
adamc@152 115
adamc@152 116 Lemma weaken_lookup : forall G2 x t G',
adamc@152 117 G' # G2
adamc@152 118 -> forall G1, G1 ++ G2 |-v x : t
adamc@152 119 -> G1 ++ G' ++ G2 |-v x : t.
adamc@152 120 Hint Resolve weaken_lookup'.
adamc@152 121
adamc@152 122 induction G1 as [ | [x' t'] tl ]; crush;
adamc@152 123 match goal with
adamc@152 124 | [ H : _ |-v _ : _ |- _ ] => inversion H; crush
adamc@152 125 end.
adamc@152 126 Qed.
adamc@152 127
adamc@152 128 Hint Resolve weaken_lookup.
adamc@152 129
adamc@152 130 Lemma hasType_push : forall x t G1 G2 e t',
adamc@152 131 ((x, t) :: G1) ++ G2 |-e e : t'
adamc@152 132 -> (x, t) :: G1 ++ G2 |-e e : t'.
adamc@152 133 trivial.
adamc@152 134 Qed.
adamc@152 135
adamc@152 136 Hint Resolve hasType_push.
adamc@152 137
adamc@152 138 Theorem weaken_hasType' : forall G' G e t,
adamc@152 139 G |-e e : t
adamc@152 140 -> forall G1 G2, G = G1 ++ G2
adamc@152 141 -> G' # G2
adamc@152 142 -> G1 ++ G' ++ G2 |-e e : t.
adamc@152 143 induction 1; crush; eauto.
adamc@152 144 Qed.
adamc@152 145
adamc@152 146 Theorem weaken_hasType : forall G e t,
adamc@152 147 G |-e e : t
adamc@152 148 -> forall G', G' # G
adamc@152 149 -> G' ++ G |-e e : t.
adamc@152 150 intros; change (G' ++ G) with (nil ++ G' ++ G);
adamc@152 151 eapply weaken_hasType'; eauto.
adamc@152 152 Qed.
adamc@152 153
adamc@152 154 Theorem weaken_hasType_closed : forall e t,
adamc@152 155 nil |-e e : t
adamc@152 156 -> forall G, G |-e e : t.
adamc@152 157 intros; rewrite (app_nil_end G); apply weaken_hasType; auto.
adamc@152 158 Qed.
adamc@152 159
adamc@152 160 Theorem weaken_hasType1 : forall G e t,
adamc@152 161 G |-e e : t
adamc@152 162 -> forall x t', x ## G
adamc@152 163 -> (x, t') :: G |-e e : t.
adamc@152 164 intros; change ((x, t') :: G) with (((x, t') :: nil) ++ G);
adamc@152 165 apply weaken_hasType; crush;
adamc@152 166 match goal with
adamc@152 167 | [ H : (_, _) = (_, _) |- _ ] => injection H
adamc@152 168 end; crush; eauto.
adamc@152 169 Qed.
adamc@152 170
adamc@152 171 Hint Resolve weaken_hasType_closed weaken_hasType1.
adamc@152 172
adamc@152 173 Section subst.
adamc@152 174 Variable x : var.
adamc@152 175 Variable e1 : exp.
adamc@152 176
adamc@152 177 Fixpoint subst (e2 : exp) : exp :=
adamc@152 178 match e2 with
adamc@152 179 | Const b => Const b
adamc@152 180 | Var x' =>
adamc@152 181 if var_eq x' x
adamc@152 182 then e1
adamc@152 183 else Var x'
adamc@152 184 | App e1 e2 => App (subst e1) (subst e2)
adamc@152 185 | Abs x' e' =>
adamc@152 186 Abs x' (if var_eq x' x
adamc@152 187 then e'
adamc@152 188 else subst e')
adamc@152 189 end.
adamc@152 190
adamc@152 191 Variable xt : type.
adamc@152 192 Hypothesis Ht' : nil |-e e1 : xt.
adamc@152 193
adamc@152 194 Lemma subst_lookup' : forall G2 x' t,
adamc@152 195 x' ## G2
adamc@152 196 -> (x, xt) :: G2 |-v x' : t
adamc@152 197 -> t = xt.
adamc@152 198 inversion 2; crush; elimtype False; eauto.
adamc@152 199 Qed.
adamc@152 200
adamc@152 201 Lemma subst_lookup : forall x' t G2,
adamc@152 202 x <> x'
adamc@152 203 -> forall G1, G1 ++ (x, xt) :: G2 |-v x' : t
adamc@152 204 -> G1 ++ G2 |-v x' : t.
adamc@152 205 induction G1 as [ | [x'' t'] tl ]; crush;
adamc@152 206 match goal with
adamc@152 207 | [ H : _ |-v _ : _ |- _ ] => inversion H
adamc@152 208 end; crush.
adamc@152 209 Qed.
adamc@152 210
adamc@152 211 Hint Resolve subst_lookup.
adamc@152 212
adamc@152 213 Lemma subst_lookup'' : forall G2 x' t,
adamc@152 214 x' ## G2
adamc@152 215 -> forall G1, x' ## G1
adamc@152 216 -> G1 ++ (x, xt) :: G2 |-v x' : t
adamc@152 217 -> t = xt.
adamc@152 218 Hint Resolve subst_lookup'.
adamc@152 219
adamc@152 220 induction G1 as [ | [x'' t'] tl ]; crush; eauto;
adamc@152 221 match goal with
adamc@152 222 | [ H : _ |-v _ : _ |- _ ] => inversion H
adamc@152 223 end; crush; elimtype False; eauto.
adamc@152 224 Qed.
adamc@152 225
adamc@152 226 Implicit Arguments subst_lookup'' [G2 x' t G1].
adamc@152 227
adamc@152 228 Lemma disjoint_cons : forall x x' t (G : ctx),
adamc@152 229 x ## G
adamc@152 230 -> x' <> x
adamc@152 231 -> x ## (x', t) :: G.
adamc@152 232 firstorder;
adamc@152 233 match goal with
adamc@152 234 | [ H : (_, _) = (_, _) |- _ ] => injection H
adamc@152 235 end; crush.
adamc@152 236 Qed.
adamc@152 237
adamc@152 238 Hint Resolve disjoint_cons.
adamc@152 239
adamc@152 240 Lemma shadow_lookup : forall G2 v t t' G1,
adamc@152 241 G1 |-v x : t'
adamc@152 242 -> G1 ++ (x, xt) :: G2 |-v v : t
adamc@152 243 -> G1 ++ G2 |-v v : t.
adamc@152 244 induction G1 as [ | [x'' t''] tl ]; crush;
adamc@152 245 match goal with
adamc@152 246 | [ H : nil |-v _ : _ |- _ ] => inversion H
adamc@152 247 | [ H1 : _ |-v _ : _, H2 : _ |-v _ : _ |- _ ] =>
adamc@152 248 inversion H1; crush; inversion H2; crush
adamc@152 249 end.
adamc@152 250 Qed.
adamc@152 251
adamc@152 252 Lemma shadow_hasType' : forall G2 G e t,
adamc@152 253 G |-e e : t
adamc@152 254 -> forall G1, G = G1 ++ (x, xt) :: G2
adamc@152 255 -> forall t'', G1 |-v x : t''
adamc@152 256 -> G1 ++ G2 |-e e : t.
adamc@152 257 Hint Resolve shadow_lookup.
adamc@152 258
adamc@152 259 induction 1; crush; eauto;
adamc@152 260 match goal with
adamc@152 261 | [ H : (?x0, _) :: _ ++ (x, _) :: _ |-e _ : _ |- _ ] =>
adamc@152 262 destruct (var_eq x0 x); subst; eauto
adamc@152 263 end.
adamc@152 264 Qed.
adamc@152 265
adamc@152 266 Lemma shadow_hasType : forall G1 G2 e t t'',
adamc@152 267 G1 ++ (x, xt) :: G2 |-e e : t
adamc@152 268 -> G1 |-v x : t''
adamc@152 269 -> G1 ++ G2 |-e e : t.
adamc@152 270 intros; eapply shadow_hasType'; eauto.
adamc@152 271 Qed.
adamc@152 272
adamc@152 273 Hint Resolve shadow_hasType.
adamc@152 274
adamc@152 275 Theorem subst_hasType : forall G e2 t,
adamc@152 276 G |-e e2 : t
adamc@152 277 -> forall G1 G2, G = G1 ++ (x, xt) :: G2
adamc@152 278 -> x ## G1
adamc@152 279 -> x ## G2
adamc@152 280 -> G1 ++ G2 |-e subst e2 : t.
adamc@152 281 induction 1; crush;
adamc@152 282 try match goal with
adamc@152 283 | [ |- context[if ?E then _ else _] ] => destruct E
adamc@152 284 end; crush; eauto 6;
adamc@152 285 match goal with
adamc@152 286 | [ H1 : x ## _, H2 : x ## _, H3 : _ |-v x : _ |- _ ] =>
adamc@152 287 rewrite (subst_lookup'' H2 H1 H3)
adamc@152 288 end; crush.
adamc@152 289 Qed.
adamc@152 290
adamc@152 291 Theorem subst_hasType_closed : forall e2 t,
adamc@152 292 (x, xt) :: nil |-e e2 : t
adamc@152 293 -> nil |-e subst e2 : t.
adamc@152 294 intros; change (nil ++ nil |-e subst e2 : t);
adamc@152 295 eapply subst_hasType; eauto.
adamc@152 296 Qed.
adamc@152 297 End subst.
adamc@152 298
adamc@154 299 Hint Resolve subst_hasType_closed.
adamc@154 300
adamc@154 301 Notation "[ x ~> e1 ] e2" := (subst x e1 e2) (no associativity, at level 80).
adamc@154 302
adamc@154 303 Inductive val : exp -> Prop :=
adamc@154 304 | VConst : forall b, val (Const b)
adamc@154 305 | VAbs : forall x e, val (Abs x e).
adamc@154 306
adamc@154 307 Hint Constructors val.
adamc@154 308
adamc@154 309 Reserved Notation "e1 ==> e2" (no associativity, at level 90).
adamc@154 310
adamc@154 311 Inductive step : exp -> exp -> Prop :=
adamc@154 312 | Beta : forall x e1 e2,
adamc@154 313 App (Abs x e1) e2 ==> [x ~> e2] e1
adamc@154 314 | Cong1 : forall e1 e2 e1',
adamc@154 315 e1 ==> e1'
adamc@154 316 -> App e1 e2 ==> App e1' e2
adamc@154 317 | Cong2 : forall e1 e2 e2',
adamc@154 318 val e1
adamc@154 319 -> e2 ==> e2'
adamc@154 320 -> App e1 e2 ==> App e1 e2'
adamc@154 321
adamc@154 322 where "e1 ==> e2" := (step e1 e2).
adamc@154 323
adamc@154 324 Hint Constructors step.
adamc@154 325
adamc@154 326 Theorem progress : forall G e t, G |-e e : t
adamc@154 327 -> G = nil
adamc@154 328 -> val e \/ exists e', e ==> e'.
adamc@154 329 induction 1; crush; eauto;
adamc@154 330 try match goal with
adamc@154 331 | [ H : _ |-e _ : _ --> _ |- _ ] => inversion H
adamc@154 332 end;
adamc@154 333 repeat match goal with
adamc@154 334 | [ H : _ |- _ ] => solve [ inversion H; crush; eauto ]
adamc@154 335 end.
adamc@154 336 Qed.
adamc@154 337
adamc@154 338 Theorem preservation : forall G e t, G |-e e : t
adamc@154 339 -> G = nil
adamc@154 340 -> forall e', e ==> e'
adamc@154 341 -> G |-e e' : t.
adamc@154 342 induction 1; inversion 2; crush; eauto;
adamc@154 343 match goal with
adamc@154 344 | [ H : _ |-e Abs _ _ : _ |- _ ] => inversion H
adamc@154 345 end; eauto.
adamc@154 346 Qed.
adamc@154 347
adamc@152 348 End Concrete.