On 11.06.2015 18:20, Dan Doel wrote:
I believe a pattern is classified as unfailable there if it is irrefutable or refutable only by bottom. Which of course is the distinction here, (x,y) is unfailable, but not irrefutable.
Some of the confusion may be because GHC has a function "isIrrefutableHsPat" that seems to check whether a pattern is irrefutable by your definition. The source comment talks about naming a bit:
(isIrrefutableHsPat p) is true if matching against p cannot fail, in the sense of falling through to the next pattern. (NB: this is not quite the same as the (silly) defn in 3.17.2 of the Haskell 98 report.)
Source: https://github.com/ghc/ghc/blob/c5911479f295242e16e396eb5d1369f2e4ce8de0/com... (Time for a PatternUnfallthroughableProposal?) Greetings, David