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prolog practice
A few alternate prolog tutorials, if you want more/different examples:
The easiest way to run prolog is using
swish.swi-prolog.org/, an on-line prolog interpreter.
(To use,
enter rules on the left, and queries followed by Ctrl-Enter in the lower-right.)
We saw already:
- run /usr/local/bin/xsb from rucs
- facts vs rules
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To load a file family.pl from the xsb prompt, type:
consult('family.pl')., which can be abbreviated as
[family].
warning:
Don't have spaces in your filename.
(That's maybe not too unsurprising: xsb interprets that as a list of length two.)
Also, don't have hyphens in your filename!;
xsb interprets the hyphens as subtraction, and gives a syntax error.
-
a standard family-tree example: 'father(X,Y) :- male(X), parent(X,Y).'
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Self-exercise: grandfather, w/ a partner.
(What is the def'n in English, for "Old is a grandparent of Yng"?)
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talk/reflect about how this is declarative programming
(just saying 'prolog searches for all solutions', without saying more);
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write a recursive rule: 'ancestor'.
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have them take a crack at writing with a partner:
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nth-father (generalized grandfather; call 'ancestor')
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sameLastName (or, “sameYChromosone”): check for male-only lineage
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Write cousin.
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Digress, in English:
cousin, 2nd cousin, 3rd cousin;
nth cousin m times removed.
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Write nthCousin (which detects exact nth-cousins, 0 times removed)
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Remember facts just rules w/o variables;
no intrinsic difference inside prolog.
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Helpful tips:
trace,
and see http://www.cs.toronto.edu/~joanis/324/w01/xsbprolog.txt.
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