 ### Convert some more examples.

parent 4cb75244
 ... @@ -84,8 +84,8 @@ module Grid ... @@ -84,8 +84,8 @@ module Grid (** {3 Valid Sudoku Solutions} *) (** {3 Valid Sudoku Solutions} *) (** [valid_chunk g i start offsets] is true whenever the chunk (** valid_chunk g i start offsets is true whenever the chunk denoted by [start,offsets] from cell [i] is "valid" in grid [g], in denoted by start,offsets from cell i is "valid" in grid g, in the sense that it contains at most one occurence of each number the sense that it contains at most one occurence of each number between 1 and 9 *) between 1 and 9 *) ... @@ -107,16 +107,16 @@ module Grid ... @@ -107,16 +107,16 @@ module Grid predicate valid_square (s:sudoku_chunks) (g:grid) (i:int) = predicate valid_square (s:sudoku_chunks) (g:grid) (i:int) = valid_chunk g i s.square_start s.square_offsets valid_chunk g i s.square_start s.square_offsets (** [valid g] is true when all chunks are valid *) (** valid g is true when all chunks are valid *) predicate valid (s:sudoku_chunks) (g : grid) = predicate valid (s:sudoku_chunks) (g : grid) = forall i : int. is_index i -> forall i : int. is_index i -> valid_column s g i /\ valid_row s g i /\ valid_square s g i valid_column s g i /\ valid_row s g i /\ valid_square s g i (** [full g] is true when all cells are filled *) (** full g is true when all cells are filled *) predicate full (g : grid) = predicate full (g : grid) = forall i : int. is_index i -> 1 <= Map.get g i <= 9 forall i : int. is_index i -> 1 <= Map.get g i <= 9 (** [included g1 g2] *) (** included g1 g2 *) predicate included (g1 g2 : grid) = predicate included (g1 g2 : grid) = forall i : int. is_index i /\ 1 <= Map.get g1 i <= 9 -> forall i : int. is_index i /\ 1 <= Map.get g1 i <= 9 -> Map.get g2 i = Map.get g1 i Map.get g2 i = Map.get g1 i ... @@ -132,8 +132,8 @@ module Grid ... @@ -132,8 +132,8 @@ module Grid forall s g h. forall s g h. well_formed_sudoku s /\ included g h /\ valid s h -> valid s g well_formed_sudoku s /\ included g h /\ valid s h -> valid s g (** A solution of a grid [data] is a full grid [sol] (** A solution of a grid data is a full grid sol that is valid and includes [data] *) that is valid and includes data *) predicate is_solution_for (s:sudoku_chunks) (sol:grid) (data:grid) = predicate is_solution_for (s:sudoku_chunks) (sol:grid) (data:grid) = included data sol /\ full sol /\ valid s sol included data sol /\ full sol /\ valid s sol ... @@ -248,8 +248,8 @@ module Solver ... @@ -248,8 +248,8 @@ module Solver use import array.Array use import array.Array (** [check_valid_chunk g i start offsets] checks the validity (** check_valid_chunk g i start offsets checks the validity of the chunk that includes [i] *) of the chunk that includes i *) let check_valid_chunk (g:array int) (i:int) let check_valid_chunk (g:array int) (i:int) (start:array int) (offsets:array int) : unit (start:array int) (offsets:array int) : unit requires { g.length = 81 } requires { g.length = 81 } ... @@ -283,8 +283,8 @@ module Solver ... @@ -283,8 +283,8 @@ module Solver forall j : int. 0 <= j < i -> forall j : int. 0 <= j < i -> valid_column s g j /\ valid_row s g j /\ valid_square s g j valid_column s g j /\ valid_row s g j /\ valid_square s g j (** [check_valid s g] checks if the (possibly partially filled) grid (** check_valid s g checks if the (possibly partially filled) grid [g] is valid. (This function is not needed by the solver) *) g is valid. (This function is not needed by the solver) *) let check_valid (s:sudoku_chunks) (g : array int) : bool let check_valid (s:sudoku_chunks) (g : array int) : bool requires { well_formed_sudoku s } requires { well_formed_sudoku s } requires { g.length = 81 } requires { g.length = 81 } ... @@ -302,7 +302,7 @@ module Solver ... @@ -302,7 +302,7 @@ module Solver with Invalid -> False with Invalid -> False end end (** [full_up_to g i] is true when all cells [0..i-1] in grid [g] are (** full_up_to g i is true when all cells 0..i-1 in grid g are non empty *) non empty *) predicate full_up_to (g : grid) (i : int) = forall j : predicate full_up_to (g : grid) (i : int) = forall j : int. 0 <= j < i -> 1 <= Map.get g j <= 9 int. 0 <= j < i -> 1 <= Map.get g j <= 9 ... @@ -358,31 +358,31 @@ module Solver ... @@ -358,31 +358,31 @@ module Solver (** how to prove the "hard" property : if (** how to prove the "hard" property : if [valid_up_to s g i] valid_up_to s g i and and [h = g[i <- k] (with 1 <= k <= 9)] h = g[i <- k (with 1 <= k <= 9)] and and [valid_column s h i /\ valid_row s h i /\ valid_square s h i] valid_column s h i /\ valid_row s h i /\ valid_square s h i then then [valid_up_to s h (i+1)] valid_up_to s h (i+1) then the problem is that one should prove that for each [j] in [0..i-1] : then the problem is that one should prove that for each j in 0..i-1 : [valid_column s h j /\ valid_row s h j /\ valid_square s h j] valid_column s h j /\ valid_row s h j /\ valid_square s h j this is true but with 2 different possible reasons: this is true but with 2 different possible reasons: if [column_start j = column_start i] then if column_start j = column_start i then [valid_column s h j] is true because [valid_column s h i] is true valid_column s h j is true because valid_column s h i is true else else [valid_column s h j] is true because [valid_column s g j] is true valid_column s h j is true because valid_column s g j is true because [valid_column s h j] does not depend on [h[i]] because valid_column s h j does not depend on h[i] *) *) ... ...
 ... @@ -4,9 +4,9 @@ ... @@ -4,9 +4,9 @@ We are interested in specifying and proving correct We are interested in specifying and proving correct data structures that support efficient computation of the sum of the data structures that support efficient computation of the sum of the values over an arbitrary range of an array. values over an arbitrary range of an array. Concretely, given an array of integers [a], and given a range Concretely, given an array of integers a, and given a range delimited by indices [i] (inclusive) and [j] (exclusive), we wish delimited by indices i (inclusive) and j (exclusive), we wish to compute the value: [\sum_{k=i}^{j-1} a[k]]. to compute the value: \sum_{k=i}^{j-1} a[k]. In the first part, we consider a simple loop In the first part, we consider a simple loop for computing the sum in linear time. for computing the sum in linear time. ... @@ -15,7 +15,7 @@ In the second part, we introduce a cumulative sum array ... @@ -15,7 +15,7 @@ In the second part, we introduce a cumulative sum array that allows answering arbitrary range queries in constant time. that allows answering arbitrary range queries in constant time. In the third part, we explore a tree data structure that In the third part, we explore a tree data structure that supports modification of values from the underlying array [a], supports modification of values from the underlying array a, with logarithmic time operations. with logarithmic time operations. *) *) ... @@ -28,23 +28,23 @@ module ArraySum ... @@ -28,23 +28,23 @@ module ArraySum use export int.Int use export int.Int use export array.Array use export array.Array (** [sum a i j] denotes the sum [\sum_{i <= k < j} a[k]]. (** sum a i j denotes the sum \sum_{i <= k < j} a[k]. It is axiomatizated by the two following axioms expressing It is axiomatizated by the two following axioms expressing the recursive definition the recursive definition if [i <= j] then [sum a i j = 0] if i <= j then sum a i j = 0 if [i < j] then [sum a i j = a[i] + sum a (i+1) j] if i < j then sum a i j = a[i] + sum a (i+1) j *) *) let rec function sum (a:array int) (i j:int) : int let rec function sum (a:array int) (i j:int) : int requires { 0 <= i <= j <= a.length } requires { 0 <= i <= j <= a.length } variant { j - i } variant { j - i } = if j <= i then 0 else a[i] + sum a (i+1) j = if j <= i then 0 else a[i] + sum a (i+1) j (** lemma for summation from the right: (** lemma for summation from the right: if [i < j] then [sum a i j = sum a i (j-1) + a[j-1]] if i < j then sum a i j = sum a i (j-1) + a[j-1] *) *) lemma sum_right : forall a : array int, i j : int. lemma sum_right : forall a : array int, i j : int. ... @@ -63,8 +63,8 @@ module Simple ... @@ -63,8 +63,8 @@ module Simple use import ArraySum use import ArraySum use import ref.Ref use import ref.Ref (** [query a i j] returns the sum of elements in [a] between (** query a i j returns the sum of elements in a between index [i] inclusive and index [j] exclusive *) index i inclusive and index j exclusive *) let query (a:array int) (i j:int) : int let query (a:array int) (i j:int) : int requires { 0 <= i <= j <= a.length } requires { 0 <= i <= j <= a.length } ensures { result = sum a i j } ensures { result = sum a i j } ... @@ -80,7 +80,7 @@ end ... @@ -80,7 +80,7 @@ end (** {2 Additional lemmas on [sum]} (** {2 Additional lemmas on sum} needed in the remaining code *) needed in the remaining code *) module ExtraLemmas module ExtraLemmas ... @@ -93,8 +93,8 @@ module ExtraLemmas ... @@ -93,8 +93,8 @@ module ExtraLemmas 0 <= i <= j <= k <= a.length -> 0 <= i <= j <= k <= a.length -> sum a i k = sum a i j + sum a j k sum a i k = sum a i j + sum a j k (** Frame lemma for [sum], that is [sum a i j] depends only (** Frame lemma for sum, that is sum a i j depends only of values of [a[i..j-1]] *) of values of a[i..j-1] *) lemma sum_frame : forall a1 a2 : array int, i j : int. lemma sum_frame : forall a1 a2 : array int, i j : int. 0 <= i <= j -> 0 <= i <= j -> j <= a1.length -> j <= a1.length -> ... @@ -102,8 +102,8 @@ module ExtraLemmas ... @@ -102,8 +102,8 @@ module ExtraLemmas (forall k : int. i <= k < j -> a1[k] = a2[k]) -> (forall k : int. i <= k < j -> a1[k] = a2[k]) -> sum a1 i j = sum a2 i j sum a1 i j = sum a2 i j (** Updated lemma for [sum]: how does [sum a i j] changes when (** Updated lemma for sum: how does sum a i j changes when [a[k]] is changed for some [k] in [[i..j-1]] *) a[k] is changed for some k in [i..j-1] *) lemma sum_update : forall a:array int, i v l h:int. lemma sum_update : forall a:array int, i v l h:int. 0 <= l <= i < h <= a.length -> 0 <= l <= i < h <= a.length -> sum (a[i<-v]) l h = sum a l h + v - a[i] sum (a[i<-v]) l h = sum a l h + v - a[i] ... @@ -135,7 +135,7 @@ module CumulativeArray ... @@ -135,7 +135,7 @@ module CumulativeArray c.length = a.length + 1 /\ c.length = a.length + 1 /\ forall i. 0 <= i < c.length -> c[i] = sum a 0 i forall i. 0 <= i < c.length -> c[i] = sum a 0 i (** [create a] builds the cumulative array associated with [a]. *) (** create a builds the cumulative array associated with a. *) let create (a:array int) : array int let create (a:array int) : array int ensures { is_cumulative_array_for result a } ensures { is_cumulative_array_for result a } = let l = a.length in = let l = a.length in ... @@ -146,8 +146,8 @@ module CumulativeArray ... @@ -146,8 +146,8 @@ module CumulativeArray done; done; s s (** [query c i j a] returns the sum of elements in [a] between (** query c i j a returns the sum of elements in a between index [i] inclusive and index [j] exclusive, in constant time *) index i inclusive and index j exclusive, in constant time *) let query (c:array int) (i j:int) (ghost a:array int): int let query (c:array int) (i j:int) (ghost a:array int): int requires { is_cumulative_array_for c a } requires { is_cumulative_array_for c a } requires { 0 <= i <= j < c.length } requires { 0 <= i <= j < c.length } ... @@ -155,8 +155,8 @@ module CumulativeArray ... @@ -155,8 +155,8 @@ module CumulativeArray = c[j] - c[i] = c[j] - c[i] (** [update c i v a] updates cell [a[i]] to value [v] and updates (** update c i v a updates cell a[i] to value v and updates the cumulative array [c] accordingly *) the cumulative array c accordingly *) let update (c:array int) (i:int) (v:int) (ghost a:array int) : unit let update (c:array int) (i:int) (v:int) (ghost a:array int) : unit requires { is_cumulative_array_for c a } requires { is_cumulative_array_for c a } requires { 0 <= i < a.length } requires { 0 <= i < a.length } ... @@ -290,7 +290,7 @@ module CumulativeTree ... @@ -290,7 +290,7 @@ module CumulativeTree = if i=j then 0 else query_aux t a i j = if i=j then 0 else query_aux t a i j (** frame lemma for predicate [is_tree_for] *) (** frame lemma for predicate is_tree_for *) lemma is_tree_for_frame : forall t:tree, a:array int, k v i j:int. lemma is_tree_for_frame : forall t:tree, a:array int, k v i j:int. 0 <= k < a.length -> 0 <= k < a.length -> k < i \/ k >= j -> k < i \/ k >= j -> ... @@ -343,10 +343,10 @@ module CumulativeTree ... @@ -343,10 +343,10 @@ module CumulativeTree (** {2 complexity analysis} (** {2 complexity analysis} We would like to prove that [query] is really logarithmic. This is We would like to prove that query is really logarithmic. This is non-trivial because there are two recursive calls in some cases. non-trivial because there are two recursive calls in some cases. So far, we are only able to prove that [update] is logarithmic So far, we are only able to prove that update is logarithmic We express the complexity by passing a credit'' as a ghost We express the complexity by passing a credit'' as a ghost parameter. We pose the precondition that the credit is at least parameter. We pose the precondition that the credit is at least ... @@ -384,7 +384,7 @@ module CumulativeTree ... @@ -384,7 +384,7 @@ module CumulativeTree end end (** [update_aux] function instrumented with a credit *) (** update_aux function instrumented with a credit *) use import ref.Ref use import ref.Ref ... @@ -419,14 +419,14 @@ module CumulativeTree ... @@ -419,14 +419,14 @@ module CumulativeTree (Node {ind with isum = ind.isum + delta} l r',delta) (*>*) (Node {ind with isum = ind.isum + delta} l r',delta) (*>*) end end (** [query_aux] function instrumented with a credit *) (** query_aux function instrumented with a credit *) let rec query_aux_complexity (t:tree) (ghost a: array int) let rec query_aux_complexity (t:tree) (ghost a: array int) (i j:int) (ghost c:ref int) : int (i j:int) (ghost c:ref int) : int requires { is_tree_for t a t.indexes.low t.indexes.high } requires { is_tree_for t a t.indexes.low t.indexes.high } requires { 0 <= t.indexes.low <= i < j <= t.indexes.high <= a.length } requires { 0 <= t.indexes.low <= i < j <= t.indexes.high <= a.length } variant { t } variant { t } ensures { !c - old !c <= ensures { !c - old !c <= if i = t.indexes.low /\ j = t.indexes.high then 1 else if i = t.indexes.low /\ j = t.indexes.high then 1 else if i = t.indexes.low \/ j = t.indexes.high then 2 * depth t else if i = t.indexes.low \/ j = t.indexes.high then 2 * depth t else 4 * depth t } 4 * depth t } ... ...
 ... @@ -160,26 +160,26 @@ module HeightSmallSpace ... @@ -160,26 +160,26 @@ module HeightSmallSpace (** Count number of leaves in a tree. *) (** Count number of leaves in a tree. *) function leaves (t: tree 'a) : int = 1 + size t function leaves (t: tree 'a) : int = 1 + size t (** [height_limited acc depth lim t]: (** height_limited acc depth lim t: Compute the [height t] if the number of leaves in [t] is at most [lim], Compute the height t if the number of leaves in t is at most lim, fails otherwise. [acc] and [depth] are accumulators. fails otherwise. acc and depth are accumulators. For maintaining the limit within the recursion, this routine For maintaining the limit within the recursion, this routine also send back the difference between the number of leaves and also send back the difference between the number of leaves and the limit in case of success. the limit in case of success. Method: find out one child with number of leaves at most [lim/2] using Method: find out one child with number of leaves at most lim/2 using recursive calls. If no such child is found, the tree has at recursive calls. If no such child is found, the tree has at least [lim+1] leaves, hence fails. Otherwise, accumulate the result least lim+1 leaves, hence fails. Otherwise, accumulate the result of the recursive call for that child and make a recursive tail-call of the recursive call for that child and make a recursive tail-call for the other child, using the computed difference in order to for the other child, using the computed difference in order to update [lim]. Since non-tail-recursive calls halve the limit, update lim. Since non-tail-recursive calls halve the limit, the space complexity is logarithmic in [lim]. the space complexity is logarithmic in lim. Note that as is, this has a degenerate case: Note that as is, this has a degenerate case: if the small child is extremely small, we may waste a lot if the small child is extremely small, we may waste a lot of computing time on the large child to notice it is large, of computing time on the large child to notice it is large, while in the end processing only the small child until the while in the end processing only the small child until the tail-recursive call. Analysis shows that this results in tail-recursive call. Analysis shows that this results in super-polynomial time behavior (recursion T(N) = T(N/2)+T(N-1)) super-polynomial time behavior (recursion T(N) = T(N/2)+T(N-1)) To mitigate this, we perform recursive calls on all [lim/2^k] limits To mitigate this, we perform recursive calls on all lim/2^k limits in increasing order (see process_small_child subroutine), until in increasing order (see process_small_child subroutine), until one succeed or maximal limits both fails. This way, one succeed or maximal limits both fails. This way, the time spent by a single phase of the algorithm is representative the time spent by a single phase of the algorithm is representative ... ...
 ... @@ -166,8 +166,8 @@ module RedBlackTree ... @@ -166,8 +166,8 @@ module RedBlackTree (* insertion *) (* insertion *) (** [almost_rbtree n t]: [t] may have one red-red conflict at its root; (** almost_rbtree n t: t may have one red-red conflict at its root; it satisfies [rbtree n] everywhere else *) it satisfies rbtree n everywhere else *) predicate almost_rbtree (n : int) (t : tree) = predicate almost_rbtree (n : int) (t : tree) = match t with match t with ... @@ -190,8 +190,8 @@ module RedBlackTree ... @@ -190,8 +190,8 @@ module RedBlackTree forall x: key, v: value, l r: tree, n: int. forall x: key, v: value, l r: tree, n: int. almost_rbtree n (Node Black l x v r) -> rbtree n (Node Black l x v r) almost_rbtree n (Node Black l x v r) -> rbtree n (Node Black l x v r) (** [lbalance c x l r] acts as a black node constructor, (** lbalance c x l r acts as a black node constructor, solving a possible red-red conflict on [l], using the following solving a possible red-red conflict on l, using the following schema: schema: B (R (R a x b) y c) z d B (R (R a x b) y c) z d ... @@ -216,8 +216,8 @@ module RedBlackTree ... @@ -216,8 +216,8 @@ module RedBlackTree Node Black l k v r Node Black l k v r end end (** [rbalance l x r] is similar to [lbalance], solving a possible red-red (** rbalance l x r is similar to lbalance, solving a possible red-red conflict on [r]. The balancing schema is similar: conflict on r. The balancing schema is similar: B a x (R (R b y c) z d) B a x (R (R b y c) z d) B a x (R b y (R c z d)) -> R (B a x b) y (R c z d) B a x (R b y (R c z d)) -> R (B a x b) y (R c z d) ... @@ -240,8 +240,8 @@ module RedBlackTree ... @@ -240,8 +240,8 @@ module RedBlackTree Node Black l k v r Node Black l k v r end end (* [insert x s] inserts [x] in tree [s], resulting in a possible top red-red (* insert x s inserts x in tree s, resulting in a possible top red-red conflict when [s] is red. *) conflict when s is red. *) let rec insert (t : tree) (k : key) (v : value) : tree let rec insert (t : tree) (k : key) (v : value) : tree requires { bst t /\ exists n: int. rbtree n t } requires { bst t /\ exists n: int. rbtree n t } ... @@ -265,7 +265,7 @@ module RedBlackTree ... @@ -265,7 +265,7 @@ module RedBlackTree else (* k = k' *) Node Black l k' v r else (* k = k' *) Node Black l k' v r end end (* finally [add x s] calls [insert] and recolors the root as black *) (* finally add x s calls insert and recolors the root as black *) let add (t : tree) (k : key) (v : value) : tree let add (t : tree) (k : key) (v : value) : tree requires { bst t /\ exists n:int. rbtree n t } requires { bst t /\ exists n:int. rbtree n t } ... @@ -320,7 +320,7 @@ module Vacid0 ... @@ -320,7 +320,7 @@ module Vacid0 = let (d, t) = !m in = let (d, t) = !m in try find t k with Not_found -> d end try find t k with Not_found -> d end (* the easy way: implements [remove] using [replace] *) (* the easy way: implements remove using replace *) let remove (m : ref rbt) k let remove (m : ref rbt) k requires { inv !m } requires { inv !m } ensures { inv !m /\ ensures { inv !m /\ ... ...
 ... @@ -63,13 +63,13 @@ module DancingLinks ... @@ -63,13 +63,13 @@ module DancingLinks invariant { length prev = length next = n } invariant { length prev = length next = n } by { prev = make 0 0; next = make 0 0; n = 0 } by { prev = make 0 0; next = make 0 0; n = 0 } (** node [i] is a valid node i.e. it has consistent neighbors *) (** node i is a valid node i.e. it has consistent neighbors *) predicate valid_in (l: dll) (i: int) = predicate valid_in (l: dll) (i: int) = 0 <= i < l.n /\ 0 <= l.prev[i] < l.n /\ 0 <= l.next[i] < l.n /\ 0 <= i < l.n /\ 0 <= l.prev[i] < l.n /\ 0 <= l.next[i] < l.n /\ l.next[l.prev[i]] = i /\ l.next[l.prev[i]] = i /\ l.prev[l.next[i]] = i l.prev[l.next[i]] = i (** node [i] is ready to be put back in a list *) (** node i is ready to be put back in a list *) predicate valid_out (l: dll) (i: int) = predicate valid_out (l: dll) (i: int) = 0 <= i < l.n /\ 0 <= l.prev[i] < l.n /\ 0 <= l.next[i] < l.n /\ 0 <= i < l.n /\ 0 <= l.prev[i] < l.n /\ 0 <= l.next[i] < l.n /\ l.next[l.prev[i]] = l.next[i] /\ l.next[l.prev[i]] = l.next[i] /\ ... @@ -78,8 +78,8 @@ module DancingLinks ... @@ -78,8 +78,8 @@ module DancingLinks use seq.Seq as S use seq.Seq as S function nth (s: S.seq 'a) (i: int) : 'a = S.([]) s i function nth (s: S.seq 'a) (i: int) : 'a = S.([]) s i (** Representation predicate: Sequence [s] is the list of indices of (** Representation predicate: Sequence s is the list of indices of a valid circular list in [l]. a valid circular list in l. We choose to model circular lists, since this is the way the We choose to model circular lists, since this is the way the data structure is used in Knuth's dancing links algorithm. *) data structure is used in Knuth's dancing links algorithm. *) predicate is_list (l: dll) (s: S.seq int) = predicate is_list (l: dll) (s: S.seq int) = ... @@ -90,7 +90,7 @@ module DancingLinks ... @@ -90,7 +90,7 @@ module DancingLinks (forall k': int. 0 <= k' < S.length s -> k <> k' -> nth s k <> nth s k') (forall k': int. 0 <= k' < S.length s -> k <> k' -> nth s k <> nth s k') (** Note: the code below works fine even when the list has one element (** Note: the code below works fine even when the list has one element (necessarily [i] in that case). *) (necessarily i in that case). *) let remove (l: dll) (i: int) (ghost s: S.seq int) let remove (l: dll) (i: int) (ghost s: S.seq int) requires { valid_in l i } requires { valid_in l i } requires { is_list l (S.cons i s) } requires { is_list l (S.cons i s) } ... @@ -103,10 +103,10 @@ module DancingLinks ... @@ -103,10 +103,10 @@ module DancingLinks nth (S.cons i s) (k + 1) = nth s k } (* to help SMT with triggers *) nth (S.cons i s) (k + 1) = nth s k } (* to help SMT with triggers *) let put_back (l: dll) (i: int) (ghost s: S.seq int) let put_back (l: dll) (i: int) (ghost s: S.seq int) requires { valid_out l i } (* [i] is ready to be reinserted *) requires { valid_out l i } (* i is ready to be reinserted *) requires { is_list l s } requires { is_list l s } requires { 0 < S.length s } (* [s] must contain at least one element *) requires { 0 < S.length s } (* s must contain at least one element *) requires { l.next[i] = nth s 0 <> i } (* do not link [i] to itself *) requires { l.next[i] = nth s 0 <> i } (* do not link i to itself *) ensures { valid_in l i } ensures { valid_in l i } ensures { is_list l (S.cons i s) } ensures { is_list l (S.cons i s) } = = ... ...
 ... @@ -87,7 +87,7 @@ module RelaxedPrefix ... @@ -87,7 +87,7 @@ module RelaxedPrefix type char type char val eq (x y : char) : bool ensures { result = True <-> x = y } val eq (x y : char) : bool ensures { result = True <-> x = y } (** [a1[ofs1..ofs1+len]] and [a2[ofs2..ofs2+len]] are valid sub-arrays (** a1[ofs1..ofs1+len] and a2[ofs2..ofs2+len] are valid sub-arrays and they are equal *) and they are equal *) predicate eq_array (a1: array char) (ofs1: int) predicate eq_array (a1: array char) (ofs1: int) (a2: array char) (ofs2: int) (len: int) = (a2: array char) (ofs2: int) (len: int) = ... @@ -110,7 +110,7 @@ module RelaxedPrefix ... @@ -110,7 +110,7 @@ module RelaxedPrefix exception NoPrefix exception NoPrefix (** Note regarding the code: the suggested pseudo-code is buggy, as it (** Note regarding the code: the suggested pseudo-code is buggy, as it may access [a] out of bounds. We fix it by strengthening the may access a out of bounds. We fix it by strengthening the test in the conditional. *) test in the conditional. *) let is_relaxed_prefix (pat a: array char) : bool let is_relaxed_prefix (pat a: array char) : bool ... ...
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