Michael Snoyman wrote:
Here's a theoretically simple solution to the problem. How about adding a new method to the IsString typeclass: isValidString :: String -> Bool ...whenever GHC applies OverloadedStrings in a case where the type is fully known at compile time (likely the most common case), it can run the check and- if it returns False- stop the compile.
This approach does address the real reason that OverloadedStrings is unsafe in practice: library authors sometimes feel that they must reject certain strings. This gives them a safer outlet for that, with a nice simple API. However, it requires GHC to be able to resolve the monomorphic type of the string literal at a time when it can get its hands on the appropriate isValidString method, already compiled, and call it. Seems like in GHC, at least, the implementation of that would have to involve some kind of TH magic in the background. Is this possible? Thanks, Yitz