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Reply to Moon on `Vectors versus Arrays'
- To: common-lisp at SU-AI
- Subject: Reply to Moon on `Vectors versus Arrays'
- From: Dick Gabriel <RPG at SU-AI>
- Date: Mon, 13 Sep 1982 15:33:00 -0000
The difference to a user between a vector and an array is that an array is
a general object, with many features, and a vector is a commonly used
object with few features: in the array-is-king scheme one achieves a
vector via specialization. An analogy can be made between arrays/vectors
and Swiss Army knives. A Swiss army knife is a fine piece of engineering;
and, having been at MIT for a while 10 years ago, I know that they are
well-loved there. However, though a keen chef might own a Swiss Army
knife, he uses his boning knife to de-bone - he could use his Swiss Army
knife via specialization. We all think of programs as programs, not as
categories with flow-of-control as mappings, and, though the latter
is correct, it is the cognitive overhead of it that makes us favor the
former over the latter.
To me the extra few lines of code in the compiler are meaningless (why
should a few extra lines bother the co-author of a 300-page compiler?); a
few extra lines of emitted code are not very relevant either if it comes
to that (it is , after all, an S-1). Had I been concerned with saving `a
few lines of code in the compiler' you can trust that I would have spoken
up earlier about many other things.
The only point I am arguing is that the cognitive overhead of making
vectors a degenerate array *may* be too high.