CSCI 3136 Principles of Programming Languages Logic Languages - - PowerPoint PPT Presentation

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CSCI 3136 Principles of Programming Languages Logic Languages - - PowerPoint PPT Presentation

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CSCI 3136 Principles of Programming Languages Logic Languages (Prolog) Summer 2013 Faculty of Computer Science Dalhousie University 1 / 37 Logic Programming Concepts H B 1 , B 2 , . . . , B n 2 / 37 Logic Programming Concepts H

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SLIDE 1

CSCI 3136 Principles of Programming Languages

Logic Languages (Prolog)

Summer 2013 Faculty of Computer Science Dalhousie University

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Logic Programming Concepts

  • H ← B1, B2, . . . , Bn

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Logic Programming Concepts

  • H ← B1, B2, . . . , Bn

The semantics of this are that when Bi are all true , we can deduce that H is true as well.

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Logic Programming Concepts

  • H ← B1, B2, . . . , Bn

Horn clause The semantics of this are that when Bi are all true , we can deduce that H is true as well.

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Logic Programming Concepts

  • H ← B1, B2, . . . , Bn

Horn clause The semantics of this are that when Bi are all true , we can deduce that H is true as well.

  • C ← A, B

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Logic Programming Concepts

  • H ← B1, B2, . . . , Bn

Horn clause The semantics of this are that when Bi are all true , we can deduce that H is true as well.

  • C ← A, B

D ← C

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Logic Programming Concepts

  • H ← B1, B2, . . . , Bn

Horn clause The semantics of this are that when Bi are all true , we can deduce that H is true as well.

  • C ← A, B

D ← C D ← A, B

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Logic Programming Concepts

  • H ← B1, B2, . . . , Bn

Horn clause The semantics of this are that when Bi are all true , we can deduce that H is true as well.

  • C ← A, B

D ← C Resolution D ← A, B

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Logic Programming Concepts

  • H ← B1, B2, . . . , Bn

Horn clause The semantics of this are that when Bi are all true , we can deduce that H is true as well.

  • C ← A, B

D ← C Resolution D ← A, B During resolution, free variables may acquire values through unification with expressions in matching terms.

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Prolog

  • Prolog interpreter runs in the context of a database of clauses that

are assumed to be true.

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Prolog

  • Prolog interpreter runs in the context of a database of clauses that

are assumed to be true.

  • Clauses in a Prolog database can be classified as facts or rules, each
  • f which ends with a period.

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Prolog

  • Prolog interpreter runs in the context of a database of clauses that

are assumed to be true.

  • Clauses in a Prolog database can be classified as facts or rules, each
  • f which ends with a period.

takes(jane doe, his201). takes(jane doe, csci3136). takes(ajit chandra, art302). takes(ajit chandra, csci3136). classmates(X,Y) :- takes(X,Z), takes(Y,Z).

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Prolog

  • Prolog interpreter runs in the context of a database of clauses that

are assumed to be true.

  • Clauses in a Prolog database can be classified as facts or rules, each
  • f which ends with a period.
  • A variable looks like an identifier beginning with an uppercase letter.

takes(jane doe, his201). takes(jane doe, csci3136). takes(ajit chandra, art302). takes(ajit chandra, csci3136). classmates(X,Y) :- takes(X,Z), takes(Y,Z).

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SLIDE 14

Prolog

  • Prolog interpreter runs in the context of a database of clauses that

are assumed to be true.

  • Clauses in a Prolog database can be classified as facts or rules, each
  • f which ends with a period.
  • A variable looks like an identifier beginning with an uppercase letter.
  • The scope of a variable is limited to the clause in which it appears.

There are no declarations. takes(jane doe, his201). takes(jane doe, csci3136). takes(ajit chandra, art302). takes(ajit chandra, csci3136). classmates(X,Y) :- takes(X,Z), takes(Y,Z).

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Prolog

  • Prolog interpreter runs in the context of a database of clauses that

are assumed to be true.

  • Clauses in a Prolog database can be classified as facts or rules, each
  • f which ends with a period.
  • A variable looks like an identifier beginning with an uppercase letter.
  • The scope of a variable is limited to the clause in which it appears.

There are no declarations.

  • The token :- is the implication symbol; the comma indicates “and.”

takes(jane doe, his201). takes(jane doe, csci3136). takes(ajit chandra, art302). takes(ajit chandra, csci3136). classmates(X,Y) :- takes(X,Z), takes(Y,Z).

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Prolog

  • Prolog interpreter runs in the context of a database of clauses that

are assumed to be true.

  • Clauses in a Prolog database can be classified as facts or rules, each
  • f which ends with a period.
  • A variable looks like an identifier beginning with an uppercase letter.
  • The scope of a variable is limited to the clause in which it appears.

There are no declarations.

  • The token :- is the implication symbol; the comma indicates “and.”
  • One builds a database of facts and rules and then initiates execution

by giving the Prolog interpreter/compiled program a query to be answered (i.e., goal) takes(jane doe, his201). takes(jane doe, csci3136). takes(ajit chandra, art302). takes(ajit chandra, csci3136). classmates(X,Y) :- takes(X,Z), takes(Y,Z).

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Example Program 1

takes(jane, his201). takes(jane, csci3136). takes(ajit, art302). takes(ajit, csci3136). classmates(X,Y) :- takes(X,Z), takes(Y,Z).

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Example Program 1

takes(jane, his201). takes(jane, csci3136). takes(ajit, art302). takes(ajit, csci3136). classmates(X,Y) :- takes(X,Z), takes(Y,Z). What would be the output if we run: ?- classmates(jane,X).

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Example Program 1

takes(jane, his201). takes(jane, csci3136). takes(ajit, art302). takes(ajit, csci3136). classmates(X,Y) :- takes(X,Z), takes(Y,Z). What would be the output if we run: ?- classmates(jane,X). X = jane

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Example Program 1

takes(jane, his201). takes(jane, csci3136). takes(ajit, art302). takes(ajit, csci3136). classmates(X,Y) :- takes(X,Z), takes(Y,Z). What would be the output if we run: ?- classmates(jane,X). X = jane ;

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Example Program 1

takes(jane, his201). takes(jane, csci3136). takes(ajit, art302). takes(ajit, csci3136). classmates(X,Y) :- takes(X,Z), takes(Y,Z). What would be the output if we run: ?- classmates(jane,X). X = jane ; X = jane

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Example Program 1

takes(jane, his201). takes(jane, csci3136). takes(ajit, art302). takes(ajit, csci3136). classmates(X,Y) :- takes(X,Z), takes(Y,Z). What would be the output if we run: ?- classmates(jane,X). X = jane ; X = jane ;

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Example Program 1

takes(jane, his201). takes(jane, csci3136). takes(ajit, art302). takes(ajit, csci3136). classmates(X,Y) :- takes(X,Z), takes(Y,Z). What would be the output if we run: ?- classmates(jane,X). X = jane ; X = jane ; X = ajit.

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Example Program 1-1

pr(0). pr(N) :- X is N-1, pr(X), write(N),nl.

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Example Program 1-1

pr(0). pr(N) :- X is N-1, pr(X), write(N),nl. What would be the output if we run: ?- pr(3).

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Example Program 2

mem(X,[X|_]). mem(X,[_|T]):-mem(X,T).

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Example Program 2

mem(X,[X|_]). mem(X,[_|T]):-mem(X,T). What would be the output if we run: ?- mem(2,[1,2,3]).

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Example Program 2

mem(X,[X|_]). mem(X,[_|T]):-mem(X,T). What would be the output if we run: ?- mem(2,[1,2,3]). true.

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Example Program 3

app([],A,A). app([H|T],A,[H|L]):-app(T,A,L).

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Example Program 3

app([],A,A). app([H|T],A,[H|L]):-app(T,A,L). What would be the output if we run: ?- app([a,b],[d,e],L).

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Example Program 3

app([],A,A). app([H|T],A,[H|L]):-app(T,A,L). What would be the output if we run: ?- app([a,b],[d,e],L). L = [a, b, d, e].

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Example Program 4

len([ ], 0). len([_ | T], N) :- len(T, M), N is M+1.

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Example Program 4

len([ ], 0). len([_ | T], N) :- len(T, M), N is M+1. What would be the output if we run: ?- len([a,b], L).

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Example Program 4

len([ ], 0). len([_ | T], N) :- len(T, M), N is M+1. What would be the output if we run: ?- len([a,b], L). L = 2.

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Example Program 5

len([ ], 0). len([H |T], N) :- len(T, M), N is M+H.

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Example Program 5

len([ ], 0). len([H |T], N) :- len(T, M), N is M+H. What would be the output if we run: ?- len([2,3], L).

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Example Program 5

len([ ], 0). len([H |T], N) :- len(T, M), N is M+H. What would be the output if we run: ?- len([2,3], L). L = 5.

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