infix assert panics ghc
I was repeatedly getting this:
ghc-6.8.3: panic! (the 'impossible' happened) (GHC version 6.8.3 for i386-unknown-linux): rename/RnExpr.lhs:(139,26)-(150,42): Non-exhaustive patterns in lambda
After some narrowing down, I eventually found the culprit and got a repeatable error with this minimal snippet:
import Control.Exception (assert) foo = True `assert` ()
The infixness is crucial;
assert True () compiles without difficulty. I use infix notation elsewhere, so it appears to be something special about
I was able to compile successfully if I used
-O2. I see now that was likely because the asserts are simply eliminated early.
I compiled ghc from sources, so it's barely possible I did something wrong there, but the nature of the symptoms make this doubtful.