wowus/conduit — comment on commit 009ceedc29dfb7dc7aa04ef478eba3722d735f78
File: conduit/Data/Conduit/List.hs line 333
By snoyberg:

It would be more efficient to check `ra` before pulling from `sb`, since the `rb` value may be completely ignored anyway. In practical terms, that could mean an entire system call avoided.