Re: [pure-lang-users] null

[Albert G. <Dr....@t-...>]

John Cowan wrote:
> I agree in general, but I don't know why would you want an operator
> beginning with '?'.

You never know what creative uses programmers can find for these. :)

One use I can imagine is as a kind of dereferencing (prefix or postfix)
operator. E.g., here is how you can define yourself convenient
abbreviations for the reference 'get' and 'put' functions:

  > postfix 9 ? ;
  > r::pointer? = get r if refp r;
  > let r = ref 99;
  > r?;
  99
  > infixr 0 := ;
  > r::pointer := x = put r x if refp r;
  > r := r?+1;
  100
  > r := r?+1;
  101

A potential infix use would be as an abbreviation for if-then-else, e.g.:

  > infixr 0 ? ;
  > def x?y,z = if x then y else z;
  > foo x = x!=0 ? 1/abs x, 0;
  > show foo
  foo x = if x!=0 then 1/abs x else 0;
  > foo 99; foo 0;
  0.0101010101010101
  0

Turning ? into an identifier constituent in the way you recommended
would pretty much preclude such perfectly legitimate uses.

Albert

-- 
Dr. Albert Gr"af
Dept. of Music-Informatics, University of Mainz, Germany
Email:  Dr....@t-..., ag...@mu...
WWW:    http://www.musikinformatik.uni-mainz.de/ag