1 let string_INDUCT,string_RECURSION =
2 define_type "string = String (int list)";;
4 let expression_INDUCT,expression_RECURSION = define_type
5 "expression = Literal num
7 | Plus expression expression
8 | Times expression expression";;
10 let command_INDUCT,command_RECURSION = define_type
11 "command = Assign string expression
12 | Sequence command command
13 | If expression command command
14 | While expression command";;
16 parse_as_infix(";;",(18,"right"));;
17 parse_as_infix(":=",(20,"right"));;
18 override_interface(";;",`Sequence`);;
19 override_interface(":=",`Assign`);;
20 overload_interface("+",`Plus`);;
21 overload_interface("*",`Times`);;
24 `(value (Literal n) s = n) /\
25 (value (Variable x) s = s(x)) /\
26 (value (e1 + e2) s = value e1 s + value e2 s) /\
27 (value (e1 * e2) s = value e1 s * value e2 s)`;;
29 let sem_RULES,sem_INDUCT,sem_CASES = new_inductive_definition
30 `(!x e s s'. s'(x) = value e s /\ (!y. ~(y = x) ==> s'(y) = s(y))
31 ==> sem (x := e) s s') /\
32 (!c1 c2 s s' s''. sem(c1) s s' /\ sem(c2) s' s'' ==> sem(c1 ;; c2) s s'') /\
33 (!e c1 c2 s s'. ~(value e s = 0) /\ sem(c1) s s' ==> sem(If e c1 c2) s s') /\
34 (!e c1 c2 s s'. value e s = 0 /\ sem(c2) s s' ==> sem(If e c1 c2) s s') /\
35 (!e c s. value e s = 0 ==> sem(While e c) s s) /\
36 (!e c s s' s''. ~(value e s = 0) /\ sem(c) s s' /\ sem(While e c) s' s''
37 ==> sem(While e c) s s'')`;;
41 `sem(While e c) s s' <=> if value e s = 0 then (s' = s)
42 else ?s''. sem c s s'' /\ sem(While e c) s'' s'`;;
45 let DETERMINISM = prove
46 (`!c s s' s''. sem c s s' /\ sem c s s'' ==> (s' = s'')`,
47 REWRITE_TAC[IMP_CONJ; RIGHT_FORALL_IMP_THM] THEN
48 MATCH_MP_TAC sem_INDUCT THEN REPEAT CONJ_TAC THEN REPEAT GEN_TAC THEN
49 DISCH_TAC THEN ONCE_REWRITE_TAC[sem_CASES] THEN
50 REWRITE_TAC[distinctness "command"; injectivity "command"] THEN
51 REWRITE_TAC[FUN_EQ_THM] THEN ASM_MESON_TAC[]);;
53 let wlp = new_definition
54 `wlp c q s <=> !s'. sem c s s' ==> q s'`;;
56 let terminates = new_definition
57 `terminates c s <=> ?s'. sem c s s'`;;
59 let wp = new_definition
60 `wp c q s <=> terminates c s /\ wlp c q s`;;
63 (`!c. (wp c EMPTY = EMPTY)`,
64 REWRITE_TAC[FUN_EQ_THM; wp; wlp; terminates; EMPTY] THEN MESON_TAC[]);;
66 let WP_MONOTONIC = prove
67 (`q SUBSET r ==> wp c q SUBSET wp c r`,
68 REWRITE_TAC[SUBSET; IN; wp; wlp; terminates] THEN MESON_TAC[]);;
70 let WP_DISJUNCTIVE = prove
71 (`(wp c p) UNION (wp c q) = wp c (p UNION q)`,
72 REWRITE_TAC[FUN_EQ_THM; IN; wp; wlp; IN_ELIM_THM; UNION; terminates] THEN
73 MESON_TAC[DETERMINISM]);;
76 (`!c1 c2 q. wp (c1 ;; c2) = wp c1 o wp c2`,
77 REWRITE_TAC[wp; wlp; terminates; FUN_EQ_THM; o_THM] THEN REPEAT GEN_TAC THEN
78 GEN_REWRITE_TAC (LAND_CONV o ONCE_DEPTH_CONV) [sem_CASES] THEN
79 REWRITE_TAC[injectivity "command"; distinctness "command"] THEN
80 MESON_TAC[DETERMINISM]);;
82 let correct = new_definition
83 `correct p c q <=> p SUBSET (wp c q)`;;
85 let CORRECT_PRESTRENGTH = prove
86 (`!p p' c q. p SUBSET p' /\ correct p' c q ==> correct p c q`,
87 REWRITE_TAC[correct; SUBSET_TRANS]);;
89 let CORRECT_POSTWEAK = prove
90 (`!p c q q'. correct p c q' /\ q' SUBSET q ==> correct p c q`,
91 REWRITE_TAC[correct] THEN MESON_TAC[WP_MONOTONIC; SUBSET_TRANS]);;
93 let CORRECT_SEQ = prove
95 correct p c1 r /\ correct r c2 q ==> correct p (c1 ;; c2) q`,
96 REWRITE_TAC[correct; WP_SEQ; o_THM] THEN
97 MESON_TAC[WP_MONOTONIC; SUBSET_TRANS]);;