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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