[riffraff]

pardon my ignorance, but what would be the difference between the two? Don't rewrite rules happen in GCH anyway?

[DanWaterworth]

Sorry, I should have been clearer. The rewriting happens in GHC, but it's the application programmer who creates the rules. So, stream fusion isn't implemented by the compiler AFAIK.

[riffraff]

ah that makes sense, thanks.