Declarative Programming Some Prolog Examples

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Declarative ProgrammingSome Prolog Examples

• Aleksander Sadikov, Ivan Bratko
• Faculty of Computer and Information Science
• University of Ljubljana

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Non-deterministic automaton
b
a
a
null
null
b
b
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• automaton definition
• final(s3).
• trans(s1, a, s1).
• trans(s1, a, s2).
• trans(s1, b, s1).
• trans(s2, b, s3).
• trans(s3, b, s4).
• silent(s2, s4).
• silent(s3, s1).

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Simulator
(a)
null
string
(c)
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• simulator definition
• accepts(State, )-
• final(State).
• accepts(State, XRest)-
• trans(State, X, State1),
• accepts(State1, Rest).
• accepts(State, String)-
• silent(State, State1),
• accepts(State1, String).

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First Solution

• generalize the number of queens start with no
  queens and add one by one
• representation 1/Y1, 2/Y2, ..., 8/Y8
• idea X/Y Others
• no attacks within Others
• Y is bounded to interval 1..8
• queen X/Y must not attack any queen in Others

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Second Solution

• each queen is located at some square
• to be safe it has to be on a separate
• column, row, upward and downward diagonal
• use a richer representation with four
  coordinates!
• solution is thus select 8 4-tuples from their
  respective domains
• the elements can be taken only once from the
  domains