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Path: utzoo!linus!decvax!cca!ima!inmet!bhyde
From: bhyde@inmet.UUCP
Newsgroups: net.lang
Subject: Re: Re: Anti-CLU... Anti-Strong-Typing.. - (nf)
Message-ID: <589@inmet.UUCP>
Date: Fri, 9-Dec-83 22:42:23 EST
Article-I.D.: inmet.589
Posted: Fri Dec  9 22:42:23 1983
Date-Received: Sun, 11-Dec-83 01:14:20 EST
Lines: 29

#R:vax2:-81700:inmet:4700013:000:1268
inmet!bhyde    Dec  3 22:30:00 1983

It seems very reasonable that the compiler should be able to sweep over
the input a couple times.  Ada is full of stuff to avoid this, the form
of an object must be bound in the same compilation unit as its first
use.  On this topic; Ada's elaboration before use rules are particularly
interesting.

The problem with not doing this is that at worst the entire program
must be available to the compiler.  Programs are big, and the data
structures that compilers build to describe them are much bigger.

Another problem is that the compiler then has to check for cyclic
dependencies; records including instances themselves, generics
including instances of themselves.  The range of such a check can be
very large, again the compiler may have to cover quite a scope to ckeck
for them.  Ada includes a few such checks, to make the check tractable
the closure computation must be done incrementally as each compilation
unit arrives and the program library is decorated with the partially
completed computation.

Quiz, is the rule that generics maynot contain instances of themselves
required in any languages?

It would be fun to attempt to design a production, modular (i.e.
spec's and bodies seperated), strong typed language with out these 
kind of rules.
				ben hyde