CODEWITHSUNDEEP
listprolognestedmember
Rickard
Rickard

Reputation: 1299

Check if something is a member in a nested list in Prolog

I want to check if x is a member of a nested list, so that

member(x,[a,b,[c,d],[e,[f,g],[x,i]]])

returns True, and False if there is no x. Is this possible somehow?

Upvotes: 3

Views: 5713

Answers (3)

Harshdeep Singh
Harshdeep Singh

Reputation: 337

By this you find the member in a simple list. ( _ ) -> Singleton Variable

//Base Case

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

By this you find the member in a nested list using the defination of a simple list:

nestedListMember(X, [H | T]) :- 
    member(X,H); 
    nestedListMember(X,T). %Recursive call looking in the tail
nestedListMember(X,[T]) :- 
    nestedListMember(X,T). %You look for all the subsequent cases

Upvotes: 0

lambda.xy.x
lambda.xy.x

Reputation: 4998

You can also use flatten/2 to get all elements onto the same level and then use ordinary member:

?- flatten([a,b,[c,d],[e,[f,g],[x,i]]],Xs), member(x,Xs).
Xs = [a, b, c, d, e, f, g, x, i] ;
false.

and if x is not contained:

?- flatten([a,b,[c,d],[e,[f,g],[y,i]]],Xs), member(x,Xs).
false.

Upvotes: 2

l4mpi
l4mpi

Reputation: 5149

Simply expand the normal recursive member definition by adding a clause that checks if the item is a member of the first element:

member(X, [X|_]).                 %X is first element
member(X, [L|_]) :- member(X, L). %X is member of first element
member(X, [_|T]) :- member(X, T). %X is member of tail

Upvotes: 6

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