fields/ library predicate, to return empty fields.

docs/yap.tex

@@ -8854,6 +8854,37 @@ S = ["Hello","I","am","free"] ?
 no
 @end example
 
+@item split(+@var{Line},-@var{Split})
+@findex split/2
+@snindex split/2
+@cnindex split/2
+
+Unify @var{Words} with a set of strings obtained from @var{Line} by
+using the blank characters  as separators.
+
+@item fields(+@var{Line},+@var{Separators},-@var{Split})
+@findex fields/3
+@snindex fields/3
+@cnindex fields/3
+
+Unify @var{Words} with a set of strings obtained from @var{Line} by
+using the character codes in @var{Separators} as separators for
+fields. If two separators occur in a row, the field is considered
+empty. As an example, consider:
+@example
+?- fields("Hello  I am  free"," *",S).
+
+S = ["Hello","","I","am","","free"] ?
+@end example
+
+@item fields(+@var{Line},-@var{Split})
+@findex fields/2
+@snindex fields/2
+@cnindex fields/2
+
+Unify @var{Words} with a set of strings obtained from @var{Line} by
+using the blank characters  as field separators.
+
 @item glue(+@var{Words},+@var{Separator},-@var{Line})
 @findex glue/3
 @snindex glue/3

library/lineutils.yap

@@ -5,6 +5,8 @@
 	   scan_integer/3,
 	   split/2,
 	   split/3,
+	   fields/2,
+	   fields/3,
 	   glue/3,
 	   copy_line/2,
 	   filter/3,
@@ -69,6 +71,28 @@ split(SplitCodes, [C|New], Set) -->
 	split(SplitCodes, New, Set).
 split(_, [], []) --> [].
 
+fields(String, Strings) :-
+	fields(" 	", Strings, String, []).
+
+fields(String, FieldsCodes, Strings) :-
+	dofields(FieldsCodes, First, More, String, []),
+	(
+	  First = [], More = []
+	->
+	  Strings = []
+	;
+	  Strings = [First|More]
+	).
+
+dofields(FieldsCodes, [], New.More) -->
+	[C],
+	{ member(C, FieldsCodes) }, !,
+	dofields(FieldsCodes, New, More).
+dofields(FieldsCodes, [C|New], Set) -->
+	[C], !,
+	dofields(FieldsCodes, New, Set).
+dofields(_, [], []) --> [].
+
 glue([], _, []).
 glue([A], _, A) :- !.
 glue([H|T], [B|_], Merged) :-