Path: utzoo!mnetor!uunet!husc6!mit-eddie!uw-beaver!uw-june!pardo
From: pardo@june.cs.washington.edu (David Keppel)
Newsgroups: comp.lang.misc
Subject: Displays (Was:  Var scoping in Wirth-type languages)
Message-ID: <4426@june.cs.washington.edu>
Date: 10 Mar 88 23:19:16 GMT
References: <3821@ihlpf.ATT.COM> <2791@enea.se> <3949@ihlpf.ATT.COM> <7562@sol.ARPA>
Reply-To: pardo@uw-june.UUCP (David Keppel)
Organization: U of Washington, Computer Science, Seattle
Lines: 21

In article <7562@sol.ARPA> crowl@cs.rochester.edu (Lawrence Crowl) writes:
>
>An alternative technique for accessing these variables is "display registers".
>Essentially, you have a register pointing to the current activation record for
>each level of nesting.  No pointer chasing is required.  For more details, see
>a compilers text.

(Paraphrasing) from compilers class:

    "Displays are a really great idea, but are too expensive to
    implement to be useful for Algol-class languages."

Where "too expensive" is measured in terms of the cost of maintaining
one over each procedure call versus the performance penalty for scanning
up the dynamic links.

This cost measure is not true where there is hardware support for
displays, but the implication is that your money would be better spent
somewhere else.

	;-D on  ( Golly, Gee, and Whiz )  Pardo