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From: davidm@rational.com (David Moore)
Newsgroups: comp.lang.ada
Subject: Re: "Subtract C, add Ada"
Date: 16 Jan 1995 20:20:21 GMT
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Date: 1995-01-16T20:20:21+00:00
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dewar@cs.nyu.edu (Robert Dewar) writes:

>For another example of UNIFY/CONFUSE, does Algol-68 confuse or unify the
>concepts of pointers and variables.

My vote would be for UNIFY. Algol-68 clarified many things that were
implicit in other languages. For example, Algol 68 made it clear that
in the expression:

	A:=A;

The type of A on the left has one more "ref" than the A on the right. I
have found that being cavalier about ref's is a good way to get in
a horrible mess when writing a compiler or debugger. Hence, I believe
anyone who intends to be a language implementor or lawyer should
be familiar with Algol 68.

Unfortunately, it also introduced W-Grammars which I find almost impossible 
to manipulate. They belong to level 3, or perhaps 4 in the complexity 
heirarchy of formalisms:

	Level 1 Formalism.

		You can push instances (eg simple sentences in the language)
                through the formalism in your head.

	Level 2 Formalism.

		You can push through instances on a piece of foolscap while
		sitting at your desk.

	Level 3 Formalism.

		You have to get up and clean off the whiteboard before starting.
		
	Level 4 Formalism.

		You and your colleagues have to go into a conference room and clean
		off the whiteboards. You first have to argue that the phrase 
		"Do not erase" has a scope no larger than the phrase itself.

Fortunately, there is also an "informal" report on Algol 68 which is very
readable.