Show is usually valid Haskell (at least derived instances are), and has instances for most types. This class would only be a conversion from types that *are* strings in some sense (like Text) to String. We have a (very small) package for this called 'isstring' that we use internally. It has instances for String, Text (x2) and ByteString (x2) assuming UTF8 encoding. I'd be happy to open source it if people are interested. Regards, Erik On Wed, Feb 5, 2014 at 9:13 AM, Atze van der Ploeg wrote:

Isn't toString just show?

On Feb 4, 2014 3:20 PM, "Johannes Waldmann" wrote:

...

Ben Foppa writes:

...

But do we have an inverse generic function toString defined anywhere?

well, we have: class Show a where show :: a -> String

...

likereString :: (IsString a, IsString b) => a -> b

well you probably don't want to actually convert from a to String (= List of Char) then from there to b, so it would need to be accompanied by some RULES (for specific instances of a, b) for efficiency.

This still does not answer the concern whether it is (semantically) wise to have String as the "base" concept here.

- J.W.

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I agree that exposing the isstring package would be useful. Again, I think the name IsString for the class defining fromString is very misleading, especially if we have an isstring package defining the inverse relationship (i.e. toString). More appropriate would be StringIs, though I'm not recommending changing Data.String.

That's exactly what I want, thank you! On Feb 20, 2014 2:15 AM, "Patrick Pelletier" wrote:

On 2/4/14, 5:55 AM, Ben Foppa wrote:

The reason this came up is that I'm getting pretty sick of type-juggling

...

different string types from different libraries (String, Text, various ByteStrings), especially since I have to tweak all the functions I use if a type changes; discovering fromString was fantastic, but without toString, I can't define something like

reString :: (IsString a, IsString b) => a -> b

which is great to have if your putStrLn only accepts one kind of string, and you have several distinct ones floating around.

Although it doesn't seem to be used much, I noticed that there's this package on Hackage:

http://hackage.haskell.org/package/stringable-0.1.2/docs/ Data-Stringable.html

which seems like it's addressing the same problem you're trying to solve.

--Patrick

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