Haskell's GHC offers optimisations-in-libraries via its RULES pragma[1], which allows specifying rewrite rules. These are an important part of the deforestation

Haskell's GHC offers optimisations-in-libraries via its RULES pragma[1], which allows specifying rewrite rules. These are an important part of the deforestation[2] that makes, for instance, lists and vectors fast. [1]: https://wiki.haskell.org/Playing_by_the_rules https://wiki.haskell.org/Playing_by_the_rules [2]: http://hackage.haskell.org/package/vector-0.7.1/docs/src/Data-Vector-Generic.html#line-212 http://hackage.haskell.org/package/vector-0.7.1/docs/src/Dat...