February 10th, 2009

eyes black and white

Who's responsible for that moving part?

Common Lisp pathnames have long been a source of frustration for users and implementers alike. I'll argue that the deep reason for this frustration is that the Common Lisp standardization process resulted in declaring as fixed an interface to a moving functionality, preventing users' needs to be addressed with no one in charge of addressing the discrepancy.

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Once you understand programming language documents not as mere technical documents, but as social tools to coordinate people, you can critique them from a new perspective. Who promises to whom to take responsibility for what in exchange for what? What about the contract brings value to both parties, and what doesn't? These are questions you should be asking when working on programming language design. Contracts are useful when they promote an efficient division of labor, whereby the more competent in a specialized field easily take responsibility for work in said field at the benefit of others, at low cost. Contracts are harmful when they create unnecessary work, when they assign responsibilities to the wrong people, when they impede future improvement in division of labor. Design your contracts carefully; include what works, exclude what doesn't.