98 lines
1.5 KiB
Markdown
98 lines
1.5 KiB
Markdown
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## Some basic syntax
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```
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property(name).
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proposition.
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/* rules */
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head :- tail.
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```
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Example:
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```
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happy(yolanda).
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listens2Music(mia).
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listens2Music(yolanda):- happy(yolanda).
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playsAirGuitar(mia):- listens2Music(mia).
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playsAirGuitar(yolanda):- listens2Music(yolanda).
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```
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### Rules
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Conditional fact:
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```
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/* source */
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listensToMusic(X) :- happy(X).
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playsAirGuitar(X) :- listensToMusic(X).
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happy(a).
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/* interactive */
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playsAirGuitar(a). /* true */
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playsAirGuitar(b). /* false */
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```
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## KB5
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```
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loves(vincent,mia).
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loves(marsellus,mia).
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loves(pumpkin,honey_bunny).
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loves(honey_bunny,pumpkin).
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jealous(X,Y):- loves(X,Z), loves(Y,Z).
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```
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Note that when you enter queries, sometimes it waits for you to enter something
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(so far seems like a semi-colon finishes a query). For example:
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```
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2 ?- jealous(vincent, W).
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W = vincent
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```
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Output freezes there, waiting on input. Enter the semicolon:
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```
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2 ?- jealous(vincent, W).
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W = vincent ;
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W = marsellus.
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```
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Replacing both atoms with variable:
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```
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3 ?- jealous(A, B).
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A = B, B = vincent ;
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A = vincent,
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B = marsellus ;
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A = marsellus,
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B = vincent ;
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A = B, B = marsellus ;
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A = B, B = pumpkin ;
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A = B, B = honey_bunny.
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```
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This brings up something interesting: *jealous(A, A)* is always true:
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```
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4 ?- jealous(A, A).
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A = vincent ;
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A = marsellus ;
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A = pumpkin ;
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A = honey_bunny.
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```
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Can we fix that in the definitions?
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```
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jealous(X,Y):- loves(X,Z), loves(Y,Z), X \= Y.
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```
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Now:
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```
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9 ?- jealous(A, A).
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false.
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```
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Re-reading a previous section, seems that ';' means "or".
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