On Sat, 2004-08-14 at 22:59, Erik de Castro Lopo wrote:
> Hi all,
> 
> I've got a number of defined types for which I'd like to define
> infix operators for addition, subtraction, multiplication etc.
> 
> Unfortunately since each type needs is own infix operator I'm
> running out of ideas unique operator versions for each type.
> 
> Why is it not possible to do something like:
> 
>     let ( ++ ) (a:float) (b:float) = a +. b ;;
> 
>     let ( ++ ) (a:int) (b:int) = a + b ;;

There reason, roughly, is that it is very hard to combine
type inference with overloading. It can be done (there's
a paper on Citeseer describing an algorithm). It isn't
clear what the error message quality would be though.

The GCaml solution Richard Jones mentions:

# generic plus =
  | int -> int -> int => (+)
  | float -> float -> float => (+.)
  ;;

When you use this:

plus 1 1
plus 1.0 1.0

there is only a *single* plus function,
with several explicitly given typings --
thus avoiding the problem of combining
inference with overloading neatly.

-- 
John Skaller, mailto:skaller@users.sf.net
voice: 061-2-9660-0850, 
snail: PO BOX 401 Glebe NSW 2037 Australia
Checkout the Felix programming language http://felix.sf.net



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