Greenspun's tenth rule

programming

'Any sufficiently complicated C or Fortran program contains an ad hoc, informally-specified, bug-ridden, slow implementation of half of Common Lisp.'

Philip Greenspun's quip (there are no rules one through nine) observes that large programs inevitably grow the dynamic features their language lacks: configuration interpreters, object systems, garbage collection, all reinvented badly. It is the classic argument for choosing expressive tools instead of rebuilding them by accident. The corollary is widely quoted: this includes Common Lisp implementations themselves.

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