Re: [Caml-list] Why are arithmetic functions not polymorph?

[Brian Hurt <brian.hurt@qlogic.com>]

On Fri, 23 May 2003, hermanns wrote:

> Hello,
> 
> I'm new to OCaml, so I hope my question is not to stupid.
> 
> Can anybody explain to me why the arithmetic functions ('+', '-', ...) 
> are not polymorph
> (in the sense that they have floating point equivalents '+.', '-.', 
> ...).
> I don't understand this, because comparison funtions ('<', '>', ...) 
> are polymorph.
> So, where is the problem with arithmetic functions?
> 

Type inference is the short answer.  Consider the function:

let foo a b = a + b

Without operator overloading, the type this function has is clear- + only 
operates on integers, so it's type is int->int->int.  Were I to write:

let foo a b = a +. b

now the type is clearly float->float->float.

The comparison operators call a generic- and comparitively expensive-
comparison function.  If you know that you are only going to be comparing 
(for example) ints, it's oftentimes faster to explicitly state the types 
involved, like:

let foo (a: int) (b: int) = a < b

This allows the compiler to replace the call to the expensive comparison 
function with a cheap inline integer comparison.

Brian
  


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