is broken. Looks like it needs to use the Some tag instead of Just.
PS - is this doc somewhere in source form? I'm happy to submit PR/patch.
alan@gazebo:~$ java -jar ~/Downloads/yeti.jar
Yeti 0.9.9.1+ REPL.
> catSome [Just 3, None (), Just 1, Just 4, None ()]
1:9: Cannot apply list?<None. () | Some. 'a> -> list<'a> function (catSome) to list<Just number | None ()> argument
Type mismatch: None. () | Some. 'a => Just number | None () (member missing: Just)