CODEWITHSUNDEEP
prolog
bluedream
bluedream

Reputation: 1069

Prolog Comparisation problem

anyone have idea how to solve this problem

counts the number of occurrences of an operator inside an expression. For instance, the query:

?- count(a+b*c-(2+3*4)/(5*(2+a)+(b+c)^f((d-e)*(x-y))), *, C).

would count the number of occurrences of operator * in the expression given as the first argument and output on C

I am using SWI-prolog

Upvotes: 1

Views: 148

Answers (1)

Nicholas Carey
Nicholas Carey

Reputation: 74277

Is this homework?

Here's some hints:

  • Prolog operators are syntactic sugar around normal prolog terms. The expression 3 * 2 + 1 is parsed as the term '+'('*'(3,2),1).

  • The built-in predicate =.. decomposes a term into a list, the head of which is the functor and the tail of which comprises the [non-decomposed] terms that are the arguments to the original term.

  • The built-in predicate functor/3 unifies a term with its functor and arity.

  • You might also want to look at arg/3 which provide the means to examine the arguments of the specified term by ordinal position.

Now that you know that, a fairly simple recursive solution should present itself. If you need to factor in the arity of the desired operator, it's a little more convoluted (but not much).

Upvotes: 2

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