[Haskell-cafe] read "2" in a "void" context?

David Kraeutmann kane at kane.cx
Fri May 27 18:38:23 UTC 2016


GHCi enables -XExtendedDefaultRules, which cause read "2" to default to ().
On 5/27/2016 8:28 PM, Erik Rantapaa wrote:
> Hi fellow Haskellers!
>
> If I bring up ghci and evaluate `read 2` I get the error "Prelude.read: no
> parse"
>
> GHCi, version 7.10.2: http://www.haskell.org/ghc/  :? for help
> Prelude> read "2"
> *** Exception: Prelude.read: no parse
>
> Exactly how is this message coming about? I understand that `read` needs a
> return type in order to determine which type class instance to run. So, in
> this case, which type is `read` being asked to return?
>
> Thanks,
> Erik
>
>
>
>
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