Add float support.

[whagsv]

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Adds a new type for which numeric operations mixing ints/floats are defined. Sure could use some refactoring but fuck me if I know why ghc would not let me.

Quite ad hoc. Ought to be a nicer way to do this. Something something typeclasses?

[steffahn]

You could add something like

numValToFloat :: NumVal -> Float
numValToFloat (Float f) = f
numValToFloat (Integer i) = fromInteger i

to make all the other functions a lot shorter, e.g.

(+) (Integer a) (Integer b) = Integer $ a+b
(+) a b = Float $ (numValToFloat a)+(numValToFloat b)

also note that you can define infix operators without writing them prefix, like so:

Integer a + Integer b = Integer $ a + b
a + b = Float $ numValToFloat a + numValToFloat b

finally, adding tests would probably be a good idea ^^