Abstract patterns

Bjorn Gustavsson bjorn@REDACTED
Mon Mar 13 15:08:27 CET 2006

If you tell me where I can find the latest version of the paper,
I'll have another look at it.

What I meant by the phrase "implement efficiently" is that performance
should be comparable to that of records. If that indeed would be possible
to achive without inlining, we would be more interested in implementing
abstract patterns.


"Richard A. O'Keefe" <ok@REDACTED> writes:

> Bjorn Gustavsson <bjorn@REDACTED> wrote:
> 	Abstract patterns is tricky to implement efficiently as it would
> 	require inlining across module boundaries.
> Sorry, but as the inventor of abstract patterns, I can tell you
> that this is QUITE UNTRUE.  Abstract patterns were designed so that
> they can be implemented *either* by inline code *or* by out-of-line
> code.  At least one version of the paper explained how to do this.
> What's more, records *also* require inlining across module boundaries,
> it's just that the modules involved as called ".hrl files" and the
> inlining is done by the preprocessor.
> 	Inlining across modules boundaries with retained semantics for
> 	code change is possible to implement, but tricky.
> I repeat, you are ALREADY doing this for records and macros; the only
> difference is that with records and macros you didn't even TRY to get
> the semantics for code change right.
> Several years ago I proposed splitting -import into -import and
> -import_early, where importing a module early would create a recorded
> dependency between the two modules so that if the imported module were
> reloaded the corresponding version of the importing module would need
> reloading too.  This would permit inlining of stuff declared in
> -import_early modules.  Wouldn't this be a problem in practice?  No,
> it would be a step forward because this one-way dependency ALREADY
> exists between .hrl files and the .erl files that include them.  So
> telling the system what the xxxx is going on would create no worse
> dependency problem that already exists and would actually make life
> easier by enabling the system to tell you when you tried to make an
> inconsistent reload.
> Not that this matters, because ABSTRACT PATTERNS DO NOT NEED INLINING.
> They were consciously and explicitly designed *not* to have the same
> problems as records.
> 	Currently, we have no plans to implement abstract patterns.
> I would be happy to discuss this particular or any other apparent
> obstacle to implementing them.

Björn Gustavsson, Erlang/OTP, Ericsson AB

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