String literals

[Lennart Augustsson]

Oh, I'll take booleans too!  But those are easier to fudge with the  
existing prelude (which I have).

On Nov 13, 2006, at 12:27 , Simon Peyton-Jones wrote:

> In my experience I've seen more requests for overloaded *Boolean*  
> literals than strings.  In a Fran context, for example.
>
> Simon
>
> | -----Original Message-----
> | From: haskell-prime-bounces at haskell.org [mailto:haskell-prime- 
> bounces at haskell.org] On Behalf Of
> | Lennart Augustsson
> | Sent: 11 November 2006 03:49
> | To: Haskell Prime
> | Subject: String literals
> |
> | I think it's time that string literals got overloaded just like
> | numeric literals.  There are several reasons for this.  One  
> reason is
> | the new fast string libraries.  They are great, but string literals
> | don't work; you need to pack them first.  Another reason is the
> | increasing use of Haskell for DSELs.  In a DSEL you might want  
> string
> | literals to have a different type than the ordinary String.
> |
> | I have not implemented anything yet, but I would like to see
> | something along the lines of the following:
> |
> | class IsString s where
> |      fromString :: String -> s
> | instance IsString String where
> |      fromString = id
> |
> | The instance declaration is not allowed in Haskell-98, but it can be
> | rewritten as
> | class IsChar c where  -- Make this class local to it's defining  
> module
> |      fromChar :: Char -> c
> | instance IsChar Char where
> |      fromChar = id
> | instance (IsChar c) => IsString [c] where
> |      fromString = map fromChar
> |
> | And, like with numeric literals, any string literal will then  
> have an
> | implicit fromString insert to make the right conversion.
> |
> | My guess is that the defaulting mechanism needs to be extended to
> | default to the String type as well, or we'll get some ambiguous
> | expressions.
> |
> | Any thoughts?
> |
> |         -- Lennart
> |
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