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adamc@193
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1 (* Copyright (c) 2008, Adam Chlipala
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2 * All rights reserved.
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3 *
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4 * Redistribution and use in source and binary forms, with or without
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5 * modification, are permitted provided that the following conditions are met:
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6 *
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7 * - Redistributions of source code must retain the above copyright notice,
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8 * this list of conditions and the following disclaimer.
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9 * - Redistributions in binary form must reproduce the above copyright notice,
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10 * this list of conditions and the following disclaimer in the documentation
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11 * and/or other materials provided with the distribution.
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12 * - The names of contributors may not be used to endorse or promote products
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13 * derived from this software without specific prior written permission.
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14 *
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15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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16 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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17 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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18 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
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19 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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20 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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21 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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22 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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23 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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24 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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25 * POSSIBILITY OF SUCH DAMAGE.
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26 *)
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27
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28 (* Utility code for implementing comparisons *)
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29
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30 structure Order :> ORDER = struct
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31
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32 fun join (o1, o2) =
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33 case o1 of
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34 EQUAL => o2 ()
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35 | v => v
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36
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37 fun joinL f (os1, os2) =
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38 case (os1, os2) of
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39 (nil, nil) => EQUAL
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40 | (nil, _) => LESS
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41 | (h1 :: t1, h2 :: t2) =>
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42 join (f (h1, h2), fn () => joinL f (t1, t2))
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43 | (_ :: _, nil) => GREATER
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44
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45 fun joinO f (v1, v2) =
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46 case (v1, v2) of
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47 (NONE, NONE) => EQUAL
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48 | (NONE, _) => LESS
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49 | (_, NONE) => GREATER
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50
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51 | (SOME v1, SOME v2) => f (v1, v2)
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52
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53 end
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