[Haskell-cafe] Proposal: Rational read

[Erik Hesselink]

On 14 August 2016 at 16:00, Sean Leather <sean.leather at gmail.com> wrote:
> On Sun, Aug 14, 2016 at 9:48 PM, Tom wrote:
>>
>> Is there a reason to not allow '.' as a separator for Rational's Read
>> instance, so that both "1%2" and "0.5" can be read?
>
> While it would make read :: String -> Rational more convenient, I'm not sure
> it would be a good idea to have read accept input that will never be
> produced by show :: Rational -> String.

This already happens everywhere, right? For example, if you have a Foo
{ bar :: Int, baz :: String } with the derived read instance, this
works:

read "Foo{bar=0x01,      baz     =      \"h\101llo\"}" :: Foo

Erik