notes-computer-programming-programmingLanguageDesign-prosAndCons-immutableData

" We tried hard to find good motivations for using an ephemeral data structure when you can just as easily (actually, much more easily) use a persistent one. As we went through them, we realized that all of the standard arguments are questionable or false. The usual one is some vague notion of “efficiency” in either time or space. While I concede that one can, in principle, solve a particular, confined problem more efficiently by doing absolutely everything by hand (memory management, scheduling, arithmetic), in the overwhelming majority of cases the demands of evolution of code far outweigh the potential advantages of doing everything by hand. " -- http://existentialtype.wordpress.com/2011/04/09/persistence-of-memory/ (by "ephemeral" he means "mutable")