On Fri, Oct 28, 2011 at 11:44 AM, Carl Eastlund <c...@ccs.neu.edu> wrote: > On Fri, Oct 28, 2011 at 12:07 PM, John Clements > <cleme...@brinckerhoff.org> wrote: >> >> On Oct 28, 2011, at 8:12 AM, Joe Marshall wrote: >> >>> On Wed, Oct 26, 2011 at 8:32 PM, Dan Grossman <d...@cs.washington.edu> >>> wrote: >>>> Very minor point, but is there a rationale beyond historical precedent >>>> for + and * to allow any number of arguments but, =, <=, <, >, >= to >>>> require at least two arguments? >>> >>> 0 is the additive identity. 1 is the multiplicative identity. >>> What is the equality identity? >> >> No, I don't buy that. operators in \alpha X \alpha -> \beta can never have >> identities, but that doesn't mean they can't be generalized. >> >> I can definitely imagine that you would choose to disallow unary use of >> comparison operations to prevent a certain class of programming errors, but >> it seems pretty clear to me that the generalization of, e.g., <= is "is >> every sequential pair of items in the argument list related by the given >> operator." >> >> Am I missing something here? >> >> John > > Furthermore, that generalization is useful, as it makes (apply <= xs) > into a simple implementation of "is xs monotonically non-decreasing?", > just as (apply + xs) implements "the sum of the elements of xs". If > <= must accept 2 or more arguments (or even 1 or more), that does not > work for all lists. Personally, I'd prefer if <= and friends were > generalized. It seems more in tune with Racket's permissive Scheme > heritage -- if append accepts "improper" lists, + mixes precise > numbers with floating point, and all values act as booleans, why can't > <= accept 0 or 1 arguments?
Does this rationale also suggest that it is fine that (cdr '()) = '()? Robby _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
