They must be used once and exactly once, no more or less. I liked this paper: http://www.cs.utexas.edu/~hunt/research/hash-cons/hash-cons-papers/BakerLinearLi

They must be used once and exactly once, no more or less. I liked this paper: http://www.cs.utexas.edu/~hunt/research/hash-cons/hash-cons-papers/BakerLinearLisp.pdf http://www.cs.utexas.edu/~hunt/research/hash-cons/hash-cons-... And previous discussion: https://news.ycombinator.com/item?id=20369522 https://news.ycombinator.com/item?id=20369522