[Haskell-cafe] List as input

[Dougal Stanton]

On Fri, Oct 17, 2008 at 2:21 PM, leledumbo <leledumbo_cool at yahoo.co.id> wrote:
>
> So, what's the solution? This one:
>
> (l::[Ord]) <- readLn
>
> doesn't work (because Ord isn't a type constructor). It doesn't even comply
> to Haskell 98 standard. I want to be able to read any list of ordered
> elements.

I hope to be enlightened, but I'm pretty sure this is not possible.
Your readLn has to present a list of some specific type which can be
inferred at compile time. Which type is it? String? Int? Something
else?

Also, neither Show nor Read relate to Ord, so you cannot ever be sure
that all Readable/Showable types are Ordered, or that all Ordered
types can be Read/Shown.


D