jason.dusek:

In the paper "Stream Fusion: From Streams To Lists To Nothing At All", we find:

For large multi-module programs, the results are less clear, with just as many programs speeding up as slowing down. We find that for larger programs, GHC has a tendency to miss optimisation op- portunities for stream fusible functions across module boundaries, which is the subject of further investigation.

What's the state of these things? Is this still an issue for stream fusion?

I think it just needs rerunning in light of all the inliner changes over the past 2 years. The kinds of programs I write in practice don't seem to suffer, but I tend not to use concatMap on stream. -- Don