how to pass a list in a predicate in prolog

Question

I want to store a paragram as a list in a variable and then call that list for counting how many times a particular word appears in that paragraph.

However, when I do th

Answer 1

The line in a prolog file:

L = [hello,hello,hello].

Means to prolog:

=(L, [hello,hello,hello]).

Which means you're attempting to define a predicate, =/2. So not only will you get a singleton warning about L (since L isn't used anywhere else in this predicate definition), but you'll also see an error about an attempt to re-define the built-in =/2 since prolog already has it defined.

What you can do instead is:

my_list([hello,hello,hello]).

Then later on, you can do:

my_list(L), counthowmany(hello,L,N).

Note that this case works:

L = [hello,hello,hello], counthowmany(hello,L,N).

It works because it's not attempting to re-define =/2. It is just using the existing built-in predicate =/2.

Answer 2

You do

?- X = [hello,how,are,you,hello,hello], counthowmany(hello, X, N).
X = [hello, how, are, you, hello, hello],
N = 3.

First you first bind X ans then you ask for this specific X.

Example 2.

?- counthowmany(hello, X, N).
X = [],
N = 0.