[clean-list] Internal overloading and unboxed arrays

[David C. Norris]

Why does the commented instance declaration below fail on {#} with an 
internal overloading error, when a similar declaration for {} succeeds?

Regards,
David

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module overload

import StdEnv

class first t e :: e (t e) -> e

instance first [] e
where
    first null []  = null
    first _ [x:xs] = x

instance first {} e
where
    first null a
    | size a == 0  = null
    | otherwise    = select a 0

instance first {#} Char
where
    first null a
    | size a == 0  = null
    | otherwise    = select a 0

/* This causes error: 'internal overloading of "size" could not be solved'
instance first {#} e
where
    first null a
    | size a == 0  = null
    | otherwise    = select a 0
*/

Start :: (Char, Int, Real)
Start = (first (' ') "Hello",
        first 0 [1, 2],
        first 0.0 [1.11, 2.22])