[psuedobrain]

CEK[1] machines are very clean way of implementing continuations or other features that can be implemented in terms of them in a language with no support for lambdas or closures. they are also reasonably fast too. i implemented a simple unlambda[2] interpreter in haskell using the cek/cesk style and it was ~20% faster and more memory efficient than the fastest c interpreter i could find.

[1] https://matt.might.net/articles/cek-machines/ [2] http://www.madore.org/~david/programs/unlambda/