On Sat, Oct 30, 2021 at 9:03 PM Ralph Mellor <ralphdjmel...@gmail.com> wrote:
> On Sat, Oct 30, 2021 at 8:38 PM Sean McAfee <eef...@gmail.com> wrote: > > Anyway, pretty cool! > > I agree it's cool, at least in a golfing sense. > > But is your explanation right? > > The *range* operator (`..`), if the rhs is less than the left, > yields an empty list rather than iterating between the endpoints. > > In contrast, the *sequence* operator (`...`) iterates. > Uh. Yeah. I didn't explain why .. works for the zero-arg case and ... doesn't, because the main point of my message was about the R metaoperator and the associativity of the operator it creates. But the difference you mention is indeed exactly why .. works but ... doesn't. [*] [\*] 0...1 ==> 0 [*] [\R*] 1..0 ==> 1 To expound even further, the second expression works because 1..0 is an empty list, reducing that empty list with [\R*] produces another empty list, and reducing *that* empty list with [*] produces 1, the multiplicative identity element.
