[racket-dev] syntax-property guards? (was: Re: The Stepper strikes again)

From: Matthias Felleisen (matthias at ccs.neu.edu)
Date: Sat Aug 13 11:22:59 EDT 2011

On Aug 13, 2011, at 10:44 AM, John Clements wrote:

> That is, the code for lazy racket contains the knowledge about which things should be hidden by the stepper.  I would argue, in fact, that this is the *right* place for such knowledge. In particular, suppose you're developing the lazy stepper, and you want to say, "this thing here is hidden." How do you point to a particular expansion? You want to make an annotation in the code for the expansion itself.  The alternatives I can think of are all hideously fragile, unless you go to some AOSD approach, but I think that this would wind up being even more verbose, and not substantially less fragile.
> That is, I think that the "subtle problem" above is not actually a problem at all.

Let me try to say what I understand out loud: 

1. The existence of Stepper knowledge in the Lazy compiler creates a 'spiritual' dependency between the Lazy language and a tool in DrRacket (= Tool world). QUESTION: does this knowledge ever make sense outside of our tool suite? Could it be reused by a stack-tracing debuggger in a textual repl? 

2. At the same time, this Tool knowledge is best injected into compilation just in case we want it. QUESTION: does some knowledge about Lazy compilation move into the Stepper if we don't inject the knowledge here? 

3. I agree with John though I am actually hopeful that we can come up with a software architecture that eliminates the problem and isn't AOSD all the way. Is it possible to view this knowledge as a mixin that gets added to the Lazy compiler when the language lives in the Tool world? 

-- Matthias

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