structure references

["Walter van Roggen" <WVANROGGEN@DEC-MARLBORO.ARPA>]

With the proper declarations, something like SHIP-LENGTH does turn
into one VAX instruction, and for speed cannot check for illegal
or unusual arguments. Normally though it only checks that the
arguments are structures (or simple-vectors). It would have checked
that the type was correct, but since the type slot of a structure
might only be a subtype of the type assumed in the reference, it
would have had to do a SUBTYPEP (or the equivalent).
			---Walter
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