[Haskell-cafe] Instances of `IsString`.

Antoine Latter aslatter at gmail.com
Sun Dec 20 17:22:13 EST 2009

On Sun, Dec 20, 2009 at 4:12 PM, Brandon S. Allbery KF8NH
<allbery at ece.cmu.edu> wrote:
> On Dec 20, 2009, at 17:09 , Jason Dusek wrote:
>>  A quick check on Hayoo! and in my interpreter shows that
>>  there are basically no instances of `IsString`. Is it
>>  really so little used?
> The only 2 instances I'm aware of are String and lazy and strict
> ByteStrings.  It's not clear to me that there need to be any more (well,
> maybe the packed Unicode string package on hackage).

There's also ShowS and Text.PrettyPrint.Doc which make useful
instances. The ShowS instance is a bit dicey since ShowS is just a
type synonym. I don't know of any released packages which include
these, though.

I don't know if it would increase clarity, but I could see a Parsec
instance as well, where fromString = string :: String -> Parser
String. You could do the same for any of the parser combinator
libraries I imagine.


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