[vinkelhake]

Are there downsides to using the stream-fusion package? If not, why hasn't it been made the default so that the first naive version is fast?

[mietek]

As I understand, stream fusion is still subject of active research. A paper showing generalised stream fusion in Haskell was submitted to this year's ICFP.

There is also no benevolent dictator in charge of Haskell.

http://research.microsoft.com/en-us/um/people/simonpj/papers...

http://www.reddit.com/r/haskell/comments/1br0ls/haskell_beat...

[carterschonwald]

indeed. The generalized stream fusion work is about lifting pointwise operations to their SIMD vectorized analogue.

Likewise, stream fusion isn't always a win! Stream fusion and its siblings are great for pointwise operations, but aren't always a good idea for computations with heavy reuse, like nested convolutions or performant matrix multipy

[dons]

Complexity of concatMap operations. Nested things don't always fuse.

If you want to use fusion, the best place is the `vector` package.