default instance for IsString

[Greg Weber]

The defaulting is very good for most use cases, however I am
discovering it won't default when I try to build up a list or tuple.
This does not work:

{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE ExtendedDefaultRules #-}
{-# LANGUAGE FlexibleInstances #-}
module Default (noDefault) where
import Data.Text as T
default (T.Text)

class    NoDefault a        where noDefault :: a -> [Text]
instance NoDefault [T.Text] where noDefault = id

main = print (noDefault ["Hello!"])

On Sun, Apr 22, 2012 at 8:31 PM, Greg Weber <greg at gregweber.info> wrote:
> Sorry, someone responded on haskell-cafe and the message didn't get
> sent here. You can default a String. So this compiles just fine:
>
> {-# LANGUAGE OverloadedStrings #-}
> {-# LANGUAGE ExtendedDefaultRules #-}
> import Data.Text as T
> default (T.Text)
>
> class    NoDefault a      where noDefault :: a -> Text
> instance NoDefault T.Text where noDefault = id
>
> main = print (noDefault "Hello!")
>
> On Sun, Apr 22, 2012 at 1:57 PM, Jeremy Shaw <jeremy at n-heptane.com> wrote:
>> I have often wished for something like:
>>
>> {-# LANGUAGE StringLiteralsAs Text #-}
>>
>> where all string literals like:
>>
>>> f = "foo"
>>
>> would be translated to:
>>
>>> f = (fromString "foo" :: Text)
>>
>> I find that OverloadedStrings is too general and causes ambiguous type
>> errors. Additionally, I seldom find that I have more than one type of
>> string literal per file. Things tend to be all String, all Text, etc.
>> So, if I could just pick a concrete type for all the string literals
>> in my file, I would be happy.
>>
>> - jeremy
>>
>>
>>
>> On Sat, Apr 21, 2012 at 7:20 PM, Greg Weber <greg at gregweber.info> wrote:
>>> I would like to default IsString to use the Text instance to avoid
>>> ambiguous type errors.
>>> I see defaulting capability is available for Num. Is there any way to
>>> do this for IsString?
>>>
>>> Thanks,
>>> Greg Weber
>>>
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