On 10 July 2013 05:24, Simon Hengel
Hi, what about adding
instance IsString a => IsString (Maybe a) where fromString = Just . fromString
It makes specifying optional String/Text/... values more convenient. Here is an example that uses System.Process.shell:
Use
shell "ls -l" { cwd = "/home/me" }
instead of
shell "ls -l" { cwd = Just "/home/me" }
I'm not yet sure how essential it is. But I somehow can't see any issues with it. So why not?
+1 After reviewing the resulting discussion I agree that there's no possible ambiguity and Simon's use-case is compelling. I think it's great that this allows us to write obvious code without cluttering the common use-case with Justs, while still allowing the underlying types to be properly expressive (ie. admitting a Nothing value when that is appropriate). This is especially important for a DSL that uses lots of strings, like shell scripting. I think (Maybe String) is a perfectly good string; it's just a string type that has an extra value of Nothing -- and Nothing doesn't even play a part in the IsString instance. Conrad.