Re: Prolog list question

On Mar 29, 10:18 pm, Chip Eastham <hardm...@xxxxxxxxx> wrote:
On Mar 29, 1:55 pm, alley <edwardmus...@xxxxxxxxx> wrote:





Hello,

I have created a predicate that takes a list and a character, and
returns the elements beginning with that character:

begin_with([H|T],X) :- sub_string(H,0,1,_,X), !, write(H), nl,
begin_with(T,X).
begin_with([H|T],X) :- begin_with(T,X).

Because of the 'write(H)' clause, Prolog just outputs the elements.
How can I save the returned elements in a list like for example:

begin_with([my,name,is,martin],m,List).

and Prolog returns: List = [my,martin]
                             true.

Thanks for your help!

Think about solving this with a recursive approach,
i.e. tackling a "base" case and reducing the solution
of any longer list to a shorter one:

What result should an empty list produce?

If a list is not empty, what should we do with the
first element that, together with a call to
begin_with/2 on the tail of that list, produces
the desired result?

regards, chip- Hide quoted text -

- Show quoted text -

I added a base case: begin_with([],X). I've tried several options, but
can't get a correct implementation to save the output in a list...
.

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