On 10/03/2012 10:18 PM, Chaddaï Fouché wrote:
1.0 _is_ a Rational in the first place, it's a number literal that is not integral, so it is translated to a fraction (Rational) by the parser then converted at runtime (only once so no worry about efficiency) to the proper type in the Fractional type class by fromRational, like Double, Float, Ratio, ... Here it's a WireP () Double.
This is how this code works :
let x :: (Fractional a) => a x = 1.23 y = (3.5 :: Double) + x z = (2.7 :: Float) + x
That is good to know. I was unaware that 1.0 is parsed as a rational. Thanks for the explanation.
Note : Does GHC optimize the case were the final type is monomorphic and standard (Double, Float) if -O2 is given ? Sure one fromRational by literal shouldn't hurt much but...
I could argue that it also increased the size of the compiled executable, but I am guessing it is of little magnitude.