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? -- Matthias _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/dev
