On Thu, Aug 25, 2016 at 7:07 PM, Bradley Lucier <xxxxxx@math.purdue.edu> wrote:

I'm asking why should [disjoint types] be mandated?

Basically because Scheme does it that way. Why do we require that

strings and numbers be disjoint? In Perl, Icon, and Rexx, they are

actually the same type, but at least that's guaranteed.

Suppose that arrays may, as you say, be a disjoint type or a procedure. Then

if you write (some-array 1 2 3) instead of ((getter some-array) 1 2 3), this may

silently succeed and return some useless value if 1 2 3 are valid arguments

for the array closure. (Granted, in an unsafe Scheme you may get a crash

or a wrong result in any case.)

Additionally, a portable implementation can't use procedures for arrays anyway,

because of the `array?` procedure, which cannot have a portable implementation

in that case, since there is nothing you can portably do with a procedure

except invoke it.

So I think it is a good idea and costs nothing.

Interesting. The MIT Scheme manual gives essentially the same definitions, yet other sources basically equate reduce and fold; I understood that reduce could rely on the operation being associative.

That seems like a reasonable requirement for reduce but not for fold.

John Cowan http://www.ccil.org/~cowan xxxxxx@ccil.org

I could dance with you till the cows come home. On second thought,

I'd rather dance with the cows when you come home.

--Rufus T. Firefly