On Tue, Dec 20, 2016 at 3:53 AM, Chris Smith <cdsmith@gmail.com> 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 <dave@zednenem.com>
<http://www.eyrie.org/~zednenem/>