[racket-dev] internal-definition parsing

From: Jay McCarthy (jay.mccarthy at gmail.com)
Date: Thu Jul 8 12:09:50 EDT 2010

On Thu, Jul 8, 2010 at 11:19 AM, Matthias Felleisen
<matthias at ccs.neu.edu> wrote:
> On Jul 7, 2010, at 5:55 PM, Eli Barzilay wrote:
>> Some examples that show how useful this is:
>>  * In the lazy language you want the implicit begin to force all
>>    expressions except for the last one.
>>  * I've redefined the implicit begin (in an ugly way) for my course
>>    language to force all non-tail expressions to have a `Void' type.
>>  * The scribble/text language should really return a list of all
>>    values instead of just the last one.  It currently provides `text'
>>    that builds on `begin/collect', which allows each block of
>>    consecutive definitions to be mutually recursive -- this is now a
>>    problem in that it's different in a subtle way than the default
>>    implicit begin.
>> I think that a good goal is to have all of these uses available as
>> simple macro definitions.
>> If you take the lazy use as an example, then just a single `#%body'
>> thing is not enough: since it needs to force only expressions, then
>> having a `#%body' means that it will need to do its own crawling over
>> the expressions to find which ones are not definitions and force
>> them.  So it looks like another special #% macro would be needed, and
>> even that is not enough to implement the last one conveniently, since
>> it needs to collect all non-definition expressions and combine them.
> 1. Three distinct examples (plus Algol, which could benefit too) sound like enough.
> 2. I do not understand why #%body isn't enough. Couldn't #%body locally expand to the point where defs and exps are distinguished?
> 3. Also, I am beginning to wonder whether the right name is #%block-begin of #%body-begin
> 4. The next thing to consider is whether #%module-begin and #%block-begin are truly separate features. In a sense, we now should say that modules are just bodies. Or is there a difference?

#%module-begin as the top level controlling macro is a distinguishing
feature. Requires and provides can only be there and you know there's
only one application.


Jay McCarthy <jay at cs.byu.edu>
Assistant Professor / Brigham Young University

"The glory of God is Intelligence" - D&C 93

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