Re: [Haskell-cafe] Re: Type question in instance of a class

On Tue, 2008-11-18 at 19:05 +0100, Peter Hercek wrote:

David Menendez wrote:

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On Sun, Nov 16, 2008 at 7:09 PM, Luke Palmer wrote:

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On Sun, Nov 16, 2008 at 5:06 PM, Peter Hercek wrote:

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... and the only value the function can return is bottom. Is there any type system which would have more than one value which inhabits all types? Well something like lazy C# might; i.e. every value has a _|_ (nontermination) and null (termination but undefined).

For that matter, Control.Exception allows you to distinguish exceptional values from each other.

OK, thanks for responses. I'm not sure I understand it well so I try to summarize:

Control.Exception is an extension, also it probably cannot catch "error :: String -> a" since the report says so: http://www.haskell.org/onlinereport/exps.html#sect3.1

I think `cannot be caught by the user' is intended to be descriptive here; or, alternately, this is one place where GHC deviates from the spec. catch (error foo) h will certainly sometimes behave as h (UserError foo). Non-deterministically. jcc