[Haskell-beginners] type class for custom numeric types

[Ashish Agarwal]

I'd like to define an abstract type T, and some how make the following work:

> 3 :: T
-- allow integer literals to be read as values of type T

> 100 :: T
error: value out of bounds for type T
-- place some restrictions on which integers are valid T values

To get the first feature, is my only option to make T an instance of the Num
class? If so, I'd have to make fromIntegral return error for out of bounds
values. Is there any problem in doing that? The only law I find mentioned
for instances of Num is: abs x * signum x == x. Is this the complete
requirement?
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