CODEWITHSUNDEEP
stringprologconcatenationstring-concatenation
user2989902
user2989902

Reputation: 23

Concatenation of Strings in Prolog

I am trying to concatenate 4 strings in Prolog. I am able to concatenate 2 and 3 strings but I can't get it to work with 4. This is what I have so far:

join2(String1,String2,Newstring) :-
   name(String1,L1), name(String2,L2),
   append(L1,L2,Newlist),
   name(Newstring,Newlist).

join3(String1,String2,String3,Newstring) :-
   join2(String1,String2,S),
   join2(S,String3,Newstring).

join4(String1,String2,String3,String4,Newstring) :-
   join3(String1,String2,String3,Newstring),
     join2(String1,String2,S),
     join2(S,String3,Newstring).
   join3(Newstring,String4,Newstring).

Upvotes: 2

Views: 2069

Answers (2)

lurker
lurker

Reputation: 58244

I'm not sure what your constraints are, but you can also use SWI's append/2 and maplist/3:

concatenate(StringList, StringResult) :-
    maplist(atom_chars, StringList, Lists),
    append(Lists, List),
    atom_chars(StringResult, List).

Then you can concatenate as many as you like:

?- concatenate(["hello", ", ", "world"], String).
String = 'hello, world'.

?- concatenate(["hey, ", "you ", "don't ", "say!"], String).
String = 'hey, you don\'t say!'.

?-

Note that the above assumes you are using the default setting in SWI Prolog:

:- set_prolog_flag(double_quotes,atom).

where "abc" represents a Prolog atom and is equivalent to 'abc'.

Upvotes: 2

Scott Hunter
Scott Hunter

Reputation: 49803

You'll need at least 2 intermediate NewStrings in order to join 4 strings, but your proposed solution only uses 1 (S), although it tries to use NewString as both an intermediate and the final result.

Take what you did for join3 a step further:

join4(S1,S2,S3,S4,NS) :-
    join2(S1,S2,NS12),
    join2(S3,S4,NS34),
    join2(NS12,NS34,NS).

Upvotes: 1

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