Subject: Re: XS: possible to have side effects? From: Paul Prescod <papresco@xxxxxxxxxxxxxxxxxxxxxxxxx> Date: Sat, 07 Jun 1997 12:10:44 -0400 |
Capturing: ========== James Clark wrote: > - it is captured by an expression specifying a characteristic value; eg in > the following it would be an error if foo modified x: So that I understand the proposal more fully, could you please describe the difference between "captured by" and "used in"? Would this be a very different statement: - it is used in an expression specifying a characteristic value; I think of "capture" as what happens to free variables in old versions of Lisp without lexical scope. Could you provide your definition? Vectors: ======== Your mail seemed to imply that you are considering adding vectors to DSSSL. I'm not quite sure I understand the relationship between vectors and mutability. Why didn't ISO DSSSL have them and why would we consider them for an XS with side effects? Lazy Evaluation: ================ > In some cases an implementation will be prevented from doing an operation > lazily which it can now do lazily unless it can prove that a procedure is > side-effect free: for example, node-list-map, map-constructor. But provided > only that an implementation can identify any spec that is completely > side-effect free, which is very easy to do, no current spec need suffer > reduced performance. But how large is the effort required to provide two complete implementations of node-list-map and map-constructor? I don't see these two procedures as critical, but I do want to know what the actual likelihood of having lazy implementations of these are if side-effects were permitted. First-Class Modes: ================== > I believe this is sufficient to ensure that (process-children) and > (process-node-list) are guaranteed side-effect free. This is because the > only outside objects that are accessible to a construction rules are > top-level variables and inherited characteristic values. Keep in mind our other ideas about first-class modes. In some cases the inability to pass information down the "construction-rule tree" is painful. We should think carefully before we make it difficult or impossible to change DSSSL in the future to allow information to be passed through a (process-children). Paul Prescod DSSSList info and archive: http://www.mulberrytech.com/dsssl/dssslist
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