---- Panicz Maciej Godek <godek.mac...@gmail.com> wrote: > 2016-11-20 11:42 GMT+01:00 Jan Synáček <jan.syna...@gmail.com>: > > > > > >> Please, tell me that this is just a mistake... This can't be true. I > > >> still can't believe it. This is from 2.0.11. Please, tell me that the > > >> implementation is fixed in 2.2. > > >> > > >> Yours truly puzzled, > > > > > > > > > I don't know why you find it so puzzling. You can't take or drop > > something > > > that "isn't there" (you can't take a car or cdr from an empty list as > > well, > > > although e.g. in the language of "The Little Prover" (car '()) and (cdr > > '()) > > > both evaluate to '() to assure their totality). If you need, you can > > define > > > your own variants that take/drop at most n elements of list. > > > > Not only that you "can", it's also IMHO a fool-proof implementation > > and I can't see any reason why it should behave differently. > > > > Because someone might think that if he took 7 elements, then he has 7 > elements, so it is good that he knows earlier that this is not the case. I > don't see a point in referring to Haskell documentation when discussing > Scheme functions, though (if you try Racket, you'll note that although its > take has a reversed order of arguments compared to srfi-1, it still doesn't > allow to take or drop a positive number of elements from an empty list) > > I agree though that the srfi-1 document isn't explicit enough about this > point.
Yes. Srfi-1 ( http://srfi.schemers.org/srfi-1/srfi-1.html ) says that drop "is exactly equivalent to performing i cdr operations on x", and notes that for car and cdr "it is an error to apply them to the empty list" Also for take and drop: "For a legal i, take and drop partition the list in a manner which can be inverted with append" Implying that not all i are "legal". -Dale
