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annotate 3-Prolog/readme.txt @ 69:05871e7ac124

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Add notes on how to invoke the Sudoku code
author IBBoard <dev@ibboard.co.uk>
date Sat, 07 Oct 2017 16:50:14 +0100
parents 90c4b7f28690
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1 Installed gprolog from https://software.opensuse.org/package/gprolog
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2
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3 Some documentation says that Prolog may accept a shebang as the first line, but gprolog didn't like it.
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5 Some editors will assume ".pl" means Perl. You may need to change your syntax highlighting.
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6
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7 Running code involves calling "gprolog" without parameters and then running "['filename']." (fullstop terminates the commend).
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8 You can then query it with function calls (e.g. "likes(grommit, sheep)." in the Wallace & Grommit example). Prolog always
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9 returns "yes" or "no" at a prompt when it has finished.
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10
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11 When you ask a question with a placeholder, the placeholder has to be capitalised. Lower-case makes it an atom.
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12 When Prolog returns its answers, type ";" to get the next response or "a" to get all. Sometimes Prolog will end multiple responses
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13 with "no", sometimes with "yes". This depends on whether it needs to do more calculations to check for more answers ("no")
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14 or whether it knows it successfully gave you everything ("yes").
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16 Rules don't need to be defined once. If you define the following:
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17
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18 ancestor(X, Y) :- father(X, Y).
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19 ancestor(X, Y) :- father(X, Z), ancestor(Z, Y).
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20
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21 then Prolog will check both "definitions" of the rule.
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23 (Note: putting the recursive "ancestor/2" call at the end is called "tail recursion" and the language can optimise it to
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24 reduce call stack exhaustion issues)
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26 For the sudoku code, example invocations are:
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28 % 2×2 grid, from the book - solved correctly
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29 sudoku([_,_,2,3, _,_,_,_, _,_,_,_, 3,4,_,_], 2,2, Solution).
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31 % 2x3 grid (size suggested in the exercise)
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32 % For some reason, this one can't be perfectly solved unless certain extra values are added
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33 sudoku([_,6,_,_,_,_, 1,_,3,_,5,_, _,_,1,_,_,2, 6,_,_,4,_,_, _,5,_,3,_,1, _,_,_,_,2,_], 3, 2, Solution).
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35 % Normal 3x3 grid
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36 sudoku([_,8,3,_,4,_,_,1,7, 6,_,_,7,_,_,_,4,_, _,_,_,8,_,_,9,_,_, 8,_,5,3,7,_,_,_,_, _,_,_,1,_,9,_,_,_, _,_,_,_,8,5,3,_,9, _,_,6,_,_,8,_,_,_, _,2,_,_,_,1,_,_,3, 3,4,_,_,2,_,5,9,_ ], 3, 3, Solution).