Re: [Haskell-cafe] RebindableSyntax and fail in GHC 8

Thanks Richard, I will file the bug shortly. David, fail doesn't appear to be used at all, either for pattern match failure (which I initially expected), or for guards. Example here: https://code.world/#P2ZO5lhXKM5QGYh-vRd31Ug On Wed, Dec 21, 2016 at 12:56 PM, David Menendez wrote:

On Tue, Dec 20, 2016 at 3:53 AM, Chris Smith wrote:

...

Hey everyone,

Can someone explain to me by GHC 8 causes list comprehension bindings to desugar to use 'fail', when RebindableSyntax is enabled in GHC 8? Note that I do not have monad comprehensions enabled. If I define fail, everything works (apparently regardless of what I define fail to do?!?), but I'd like to understand why it's necessary.

Perhaps fail is used by the translation for guards. I don’t have a working GHC right now, but what happens if you define fail = error and evaluate [ x | x <- “a", False]?

-- Dave Menendez http://www.eyrie.org/~zednenem/