[racket] Question about round

On 09/29/2011 03:11 PM, Mark Engelberg wrote:
> I'm a bit baffled by this behavior:
>
>  > (exact? (round (sin 30)))
> #f
>  > (integer? (round (sin 30)))
> #t
>  >
>
> How is it possible to have an inexact integer?

 > (inexact? 1.0)
#t

The interpretation of "inexact" is subtle and contentious. But to a 
first approximation, "inexact" just means "floating-point".

To a second approximation, I interpret

   (integer? 1.0) = #t
   (inexact? 1.0) = #t

as "the representation is definitely an integer, but it may not exactly 
represent the quantity you really wanted to talk about". But I haven't 
studied this carefully, and it is possible that my interpretation is 
horribly wrong according to someone.

The pragmatic answer is you generally have to write

   (inexact->exact (round x))

which is annoying, but no one has yet bothered to add a standard library 
function for this, as far as I know.

Note also that round does not necessarily return an integer:

 > (round +inf.0)
+inf.0

Ryan