On 20 March 2013 06:58, Christopher Done wrote:

From the paper Fun with Type Funs, it's said:

...

One compelling use of such type functions is to make type coercions implicit, especially in arithmetic. Suppose we want to be able to write add a b to add two numeric values a and b even if one is an Integer and the other is a Double (without writing fromIntegral explicitly).

And then an Add class is defined which can dispatch at the type-level to appropriate functions which resolve two types into one, with a catch-all case for Num.

Has anyone put this into a package, for all common arithmetic operations? I would use it. Doing arithmetic stuff in Haskell always feels labored because of having constantly convert between number types.

hmatrix takes this approach with a Mul typeclass for combinations of Vector and Matrix multiplication, defined for things that can implement Product (real and Complex Doubles and Floats). http://hackage.haskell.org/packages/archive/hmatrix/0.14.1.0/doc/html/Numeri... I think it'd be interesting for numeric stuff to have implicit conversion to Double, using a class as you suggest which doesn't support Integral or bitops. Conrad.