Haskell function returning Integer
How do I write a function that returns everything to Integer?
ie
f True = 1
f False =0
f 1 = 1
f 2.30 = 2
The only functions of type a -> Integer will be constant functions. This is a free theorem guaranteed by the parametricity of the type (modulo some fudging because of some unsound corners of Haskell).
Here's an example of such a function:
f :: a -> Integer
f _ = 1
There's no way to do this in general, and it's not at all advisable, but the cases you mention, and some others, can be obtained using an ugly hack:
f :: Enum n => n -> Integer
f x = toInteger (fromEnum x)
As a general rule, it's best to simply pretend that the Enum class does not exist, because it is extremely badly designed and some of its instances are badly behaved.
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