This paper presents an automatic fusion system, stream fusion, based on equational transformations, that fuses a wider range of functions than existing short-cut fusion systems. In particular, stream fusion is able to fuse zips, left folds and
functions over nested lists, including list comprehensions. A distinguishing feature of the stream fusion framework is its simplicity: by transforming list functions to expose their structure, intermediate values are eliminated by general purpose compiler
We have reimplemented the entire Haskell standard list library on top of our framework, providing stream fusion for Haskell lists. By allowing a wider range of functions to fuse, we see an increase in the number of occurrences of fusion in typical
Haskell programs. We present benchmarks documenting time and space improvements.
I'd like to propose an === operator, or "is identical to" operator, unlike == it isn't overridable (so it's good for ensuring reference equality when working with types that override == without manually calling Object.ReferenceEquals). It'd also work on
structs where == is a value comparison and not a reference comparion by default.