On Wed, Apr 25, 2012 at 11:39 AM, Ozgur Akgun
One can always use a Maybe to make an IsString literal total. Perhaps this is what library authors should do in those cases when a fromString implementation is obviously partial.
i.e. instead of instance IsString XML where ... define: instance IsString (Maybe XML) where ...
HTH, Ozgur
This sounds sensible, but then you'll have to handle the Nothing case of the Maybe. There you are, writing a literal, and also writing fallback code specifying what should be done in case you messed up when writing the literal. What can you reasonably write there, other than error "oops, I wrote a bad literal"? You're back where you started. There's not much you can do about programmer error at runtime except abort, which is why you'd really prefer to have it checked at compile time. But unless you write a quasiquoter, runtime checking might be your only option, and at that point whether you prefer convenience or explicitness seems like a question of taste, because the important bad thing (runtime assertions) you're already stuck with.