Joe writes:
| Phil Writes:
|
| | The closest one can come is
| |
| | class G a where
| | g :: a -> Bool
| | g x = g [x]
| |
| | instance G Int
| | instance G [Int]
| | instance G [[Int]]
| | ...
| |
| |which requires an infinite number of instance declarations.
|
| Can't this be written as follows?
|
| instance G Int
| instance (G a) => G [a]
|
| Now, this is still an infinite number of instances, though not
| declarations, so the point still holds that it can't be monomorphized.
I don't think this works. The declaration `instance G Int' is valid
only if `instance G [Int]' holds, and this in turn requires that
`instance G [[Int]]' holds, and so on. I haven't tried it in Haskell,
but it should either be illegal or cause the type-checker to enter an
infinite loop. (Hmmm! Maybe someone should try it ...) Cheers, -- P
