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annotate 3-Prolog/readme.txt @ 58:90c4b7f28690

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Add initial Day 2 notes for Prolog
author IBBoard <dev@ibboard.co.uk>
date Tue, 26 Sep 2017 20:58:49 +0100
parents 005ae3fad18f
children 05871e7ac124
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1 Installed gprolog from https://software.opensuse.org/package/gprolog
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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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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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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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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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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)