On Mon, Jan 20, 2020 at 05:39:16AM -0500, Viktor Dukhovni wrote:
src/Hkl/Projects/Sixs.hs:67:5-35: warning: [-Wincomplete-uni-patterns] Pattern match(es) are non-exhaustive In a pattern binding: Patterns not matched: [] | 67 | cons1 !x ~(c:cs) = (x : c) : cs | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
If this is something which can not be reach, is it possible to explain to ghc how to avoid these warning ?
However, with "-Wincomplete-uni-patterns" I still get this one, but the irrefutable binding is there for a reason, stricness in the second argument has undesirable performance implications, we know that the list won't be empty. So perhaps compile this code in a module that does not have that warning turned on.
Actually, the warning can be eliminated by writing: cons1 x cs = (x : head cs) : tail cs which just as "unsafe" (we know that `cs` won't be empty, but the compiler does not), but use of the partial functions 'head' and 'tail' does not elicit a warning. The `!x` is also redundant, we've already evaluated the weight of `x`'. -- Viktor.