To follow up on my own post. I implemented the overloaded strings last night and it seems to work pretty well. I've not done anything about defaulting yet. I don't know how much of a problem this will be in practice. On Nov 10, 2006, at 22:49 , Lennart Augustsson wrote:
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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