Boolean ops on NA are broken

[johnmyleswhite]

julia> true || NA
true

julia> NA || true
ERROR: type: non-boolean (NAtype) used in boolean context

[simonster]

I'm not sure we can fix this, nor am I sure there is a unique solution. && and || are not actually functions because they short-circuit, so we can't override them for NA. The short-circuiting behavior is also conceptually problematic: It's not clear what NA || error("hello world") is supposed to do.

[johnmyleswhite]

God I hate that idiom. Will discuss with Jeff et al. later today.

[ivarne]

This is deliberate, as julia require all conditions for conditionals to be of type Bool. We could do an implicit convert(Bool, x) when the type doesn't match, but I think you'll have trouble convincing @StefanKarpinski and @JeffBezanson that it is a good idea.

Nothing prevents your from calling convert on NA manually though.

[johnmyleswhite]

This won't matter any more once NA is replaced with Nullable{Bool}. No more three-valued logic.