neeharika-sonowal / prolog-programs

Logic Progamming with Prolog

Intro to logic progamming

Logic progamming deals with relations rather than functions.

Relations

A concrete view of a relation is as a table with n>= 0 columns and a possibly infinite set of rows.

Some basic relations are:

• Rules

  Rules are written as in

      P if Q1 and Q2 and ...  and Qk. for k>=0.

  This is also called a Horn Clause.

• Facts

  A fact is a special case of a rule, in which k = 0 and P holds without any condition, written simply as

      P.

  A fact is always true.

• Append

  The append relation is specified by two rules. The first is a fact starting that triples of the form ([], Y, Y) are in relation append.

  append [] and Y to get Y.

  The second rule for append is shown for completeness. It uses the [H|T] for a list with Head H and tail T:

      append [H|X] and Y to get [H|Z]
          if append X and Y to get Z

Queries

Logic progamming is driven by queries about relation. The simplest queries ask whether a particular tuple belongs to a relation. The query asks whether the triple `([a,b],[c,d],[a,b,c,d]) belongs to relation append.

    append [a,b] and [c,d] to get [a,b,c,d]?
            Answer: yes

Intro to PROLOG