Bernie Pope
Mike, what do you mean by "willy nilly convert my error calls to bottom"?
Simon Peyton-Jones
In general, GHC (like every other compiler that does strictness analysis) feels free to change non-termination into a call to 'error' and vice versa. One could change that, but a lot of programs would become less efficient as a result.
I was concerned by the "vice versa" conversion--from an error call to non-termination. If more than one bottoms (say, a non-termination and an error call) are present in my program, I'm fine with getting any one of them. If I have only an error call, though, I do want to see an error message. An infinite loop would be unhelpful. So, I would consider it an unfriendly "willy nilly" convertion for GHC to generate code for: import System.Environment ( getArgs ) main = getArgs >>= putStrLn . head that failed to terminate when I passed no command-line arguments. -m