71 lines
1.9 KiB
Text
71 lines
1.9 KiB
Text
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(*
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* linear_search.whyml
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* WhyML implementation of byteback test `algorithm/LinearSearch`
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*)
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module LinearSearch
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use int.Int
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use ref.Ref
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use array.Array
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type t
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val predicate eq (a b : t)
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(* nullability preamble *)
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exception NullPointerException
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type nullable 't = Null | Some 't
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let predicate is_null (obj: nullable 't) =
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match obj with
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| Null -> true
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| Some _ -> false
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end
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let dereference (obj: nullable 't) : 't
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raises { NullPointerException -> is_null obj } =
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match obj with
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| Null -> raise NullPointerException
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| Some obj_val -> obj_val
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end
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(* end nullability preamble *)
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type narrt = nullable (array t)
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let predicate array_is_not_null (a: narrt) (n: t) (left right: int) = is_null a
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let predicate array_is_null (a: narrt) (n: t) (left right: int) = not (is_null a)
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let predicate bounded_indices (a: narrt) (n: t) (left right: int) =
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match a with
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| Null -> false
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| Some aa -> 0 <= left && left <= right && right <= length aa
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end
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let predicate result_is_index (a: narrt) (n: t) (left right return_val: int) =
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match a with
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| Null -> false
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| Some aa -> ((not (0 <= return_val)) || (eq aa[return_val] n))
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end
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let search (a: narrt) (n: t) (left right: int) : int
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requires { array_is_not_null a n left right }
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requires { bounded_indices a n left right }
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ensures { result_is_index a n left right result }
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raises { NullPointerException -> false }
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=
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let ref i = left in
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while i < right do
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invariant { left <= i && i <= right }
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let a_val = dereference a in
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if eq a_val[i] n then
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return i;
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i <- i + 1;
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done;
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-1
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end
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