Why do currying anonymous functions change Haskell type output from Num to Integer?

Question

I run through a Brief Introduction to Haskell and have come to currying . (So, correct all the mistakes I made in the terminology.)

This section says:

Here is a function with two arguments defined in the usual way. Prelude> let myadd x y = x + y Prelude> myadd 3 4 7

And then a little further:

Here is the third equivalent way to define myadd, since an anonymous function returns another anonymous function. Prelude> let myadd = \x -> \y -> x + y Prelude> :t myadd myadd :: Integer -> Integer -> Integer

Despite the fact that he says “equivalent”, unexpectedly (for a beginner like me), this is not so, because the type is myaddmore general:

Prelude> :t myadd
myadd :: Num a => a -> a -> a
Prelude> myadd 1.5 2.5
4.0
Prelude> myadd3 1.5 2.5

<interactive>:12:8:
    No instance for (Fractional Integer) arising from the literal `1.5'
    Possible fix: add an instance declaration for (Fractional Integer)
    In the first argument of `myadd3', namely `1.5'
    In the expression: myadd3 1.5 2.5
    In an equation for `it': it = myadd3 1.5 2.5