[Haskell-cafe] instance Enum [Char] where ...

[Adrian Neumann]

Better would be

[] = 0
['a'] = 1
['b'] = 2
...
['z'] = 26
['a','a'] = 27
['a','b'] = 28

(asuming Char = ['a'..'z'])

Am 30.12.2008 um 04:25 schrieb JustinGoguen:

> I am having difficulty making [Char] an instance of Enum. fromEnum  
> is easy
> enough: map fromEnum to each char in the string and take the sum.  
> However,
> toEnum has no way of knowing what the original string was.
>
> For example, running fromEnum on the string "d" will result in 100.  
> But when we
> pass 100 to toEnum, it does not know if it should treat 100 as "d"  
> or "22"
> (fromEnum '2' == 50).
>
> Source so far:
>
> instance Enum [Char] where
>     succ = undefined
>     pred = undefined
>     toEnum n = undefined -- what to do?
>     fromEnum xs = sum $ map fromEnum xs
>
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