yihuang/wai — comment on commit e3b7aefc49c3ec879495516cb2582396d621c269
File:  line 0
By snoyberg:

When I tested this as a replacement for mappend, the test suite hung. I believe it's running the source2 multiple times. In general, it's not safe to rerun a source after it sends an EOF, so >==> needs some mutable state to determine whether source1 has completed. Check out the implementation of mconcat.