I am currently stuck on a prolog problem.
So far I have:
film(Title) :- movie(Title,_,_). (Where 'movie(T,_,_,)' is a reference to my database)
namesearch(Title, Firstword) :- film(Title), contains_term(Firstword, Title).
It is hard to explain what I need help on, but basically is there a wildcard I can use to search for all films starting with a specific word, for example, if I were to search for all films beginning with the word "The".
Is there a wildcard which would allow me to input as such: namesearch(X,'The*') ?
I have tried using the asterisk like this and it does not work,
Thank your for your help
It all depends how the title is represented.
If it is represented as an atom, you need sub_atom(Atom, Before, Length, After, Sub_atom)
?- Title = 'The Third Man', sub_atom(Title, 0, _, _, 'The').
Title = 'The Third Man'.
If it is a list of codes which is called a string in Prologs in Edinburgh tradition, you can either "hard code" it with append/3 or you might use Definite Clause Grammars for general patterns.
?- set_prolog_flag(double_quotes,codes).
true.
?- append("The",_, Pattern), Title = "The Third Man", Pattern = Title.
Pattern = Title, Title = [84,104,101,32,84,104,105,114,100|...].
?- Title = "The Third Man", phrase(("The",...), Title).
Title = [84,104,101,32,84,104,105,114,100|...]
; false.
Note that 84 is the character code of T etc.
phrase/2 is "the entry" to grammars. See dcg for more. Above used the following definition:
... --> [] | [_], ... .
Similar to list of codes, list of characters provide a more readable representation that has still the advantages of being compatible with list predicates and Definite Clause Grammars:
?- set_prolog_flag(double_quotes,chars).
true.
?- append("The",_, Pattern), Title = "The Third Man", Pattern = Title.
Pattern = Title, Title = ['T',h,e,' ','T',h,i,r,d|...].
?- Title = "The Third Man", phrase(("The",...), Title).
Title = ['T',h,e,' ','T',h,i,r,d|...]
; false.
See also this answer.