Example of slowness compared to Bash (while or test problem?)

This is relatively quick:

```
locate $HOME | bash -c 'while read dir; do [[ -d $dir ]] && echo $dir; done'
```

But this is painfully slow:

```
function onlyDirs
    while read dir
        test -d $dir; and echo $dir
    end
end

locate $HOME | onlyDirs
```
