String matching: Difference between revisions

<lang prolog>

:- system:set_prolog_flag(double_quotes,codes) .

:- [library(lists)] .

%! starts_with(FIRSTz,SECONDz)

%

% True if `SECONDz` is the beginning of `FIRSTz` .

starts_with(FIRSTz,SECONDz)

:-

lists:append(SECONDz,_,FIRSTz)

.

%! contains(FIRSTz,SECONDz)

%

% True once if `SECONDz` is contained within `FIRSTz` at one or more positions .

contains(FIRSTz,SECONDz)

:-

contains(FIRSTz,SECONDz,_) ,

!

.

%! contains(FIRSTz,SECONDz,NTH1)

%

% True if `SECONDz` is contained within `FIRSTz` at position `NTH1` .

contains(FIRSTz,SECONDz,NTH1)

:-

lists:append([PREFIXz,SECONDz,_SUFFIXz_],FIRSTz) ,

prolog:length(PREFIXz,NTH0) ,

NTH1 is NTH0 + 1

.

%! ends_with(FIRSTz,SECONDz)

%

% True if `SECONDz` is the ending of `FIRSTz` .

ends_with(FIRSTz,SECONDz)

:-

lists:append(_,SECONDz,FIRSTz)

.

</lang>

{{out}}

<pre>

?- starts_with("abcdef","abc") .

true .

?- starts_with("abc","abc") .

true .

?- starts_with("abc","abcd") .

false .

?- starts_with("dabc","abc") .

false .

?- starts_with("","") .

true .

?-

?- contains("abcdef","abc") .

true.

?- contains("abcdef","abc",NTH).

NTH = 1 ;

false.

?- contains("abcdef","de",NTH).

NTH = 4 ;

false.

?- contains("abcdef","f",NTH).

NTH = 6 ;

false.

?- contains("abcde","f",NTH).

false.

?- contains("","",NTH).

NTH = 1 ; % wtf ?

false.

?- contains("a","a",NTH).

NTH = 1 ; % wtf ?

false.

?-

?- ends_with("abc","abc") .

true ;

false .

?- ends_with("abc","bc") .

true ;

false .

?- ends_with("abcd","bc") .

false .

?- ends_with("","") .

true ;

false .

?-

</pre>