doc-src/IsarAdvanced/Codegen/Thy/examples/example.ML
author wenzelm
Thu, 01 Jan 2009 21:30:13 +0100
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structure Example = 
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struct
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fun foldl f a [] = a
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  | foldl f a (x :: xs) = foldl f (f a x) xs;
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fun rev xs = foldl (fn xsa => fn x => x :: xsa) [] xs;
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fun list_case f1 f2 (a :: lista) = f2 a lista
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  | list_case f1 f2 [] = f1;
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datatype 'a queue = Queue of 'a list * 'a list;
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val empty : 'a queue = Queue ([], [])
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fun dequeue (Queue ([], [])) = (NONE, Queue ([], []))
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  | dequeue (Queue (xs, y :: ys)) = (SOME y, Queue (xs, ys))
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  | dequeue (Queue (v :: va, [])) =
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    let
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      val y :: ys = rev (v :: va);
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    in
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      (SOME y, Queue ([], ys))
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    end;
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fun enqueue x (Queue (xs, ys)) = Queue (x :: xs, ys);
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end; (*struct Example*)