[Haskell-cafe] Why is toRational a method of Real?

[Alexander Solla]

On Aug 4, 2010, at 11:30 AM, Omari Norman wrote:

> Why is toRational a method of Real? I thought that real numbers need  
> not
> be rational, such as the square root of two. Wouldn't it make more  
> sense
> to have some sort of Rational typeclass with this method? Thanks.

You can't build the real number field using a computer.  So you have  
to turn what "should" be a real into something you can express on a  
computer.  You can either choose to use the field of "computable real  
numbers", which is slow, or you can just go with a "near enough"  
rational approximation.