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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