I think V4 is a good step forward and I certainly welcome it.  I'm not that worried about converting my code over to it.  What I am worried about is that there doesn't seem to be a practical way, that I've seen, to maintain a single PLaneT package that is compliant with both V4 and V3.  I certainly don't see how I can make use many of the new V4 features in a PLaneT package and retain that compatibility. Doug <div class="gmail_quote">On Fri, Feb 1, 2008 at 3:53 AM, Dave Gurnell <<a href="mailto:d.j.gurnell@gmail.com">d.j.gurnell@gmail.com</a>> wrote: <blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"> <div class="Ih2E3d">> What other constructs might bite us? </div>Hi Doug, There are a lot of great improvements in PLT4, and on the whole the transition process is not too bad. However, there are a couple of areas in which I've had problems: I've been having lots of problems with keyword arguments. There is a fundamental difference in the way they work in the mzscheme and scheme/ base languages, and there are issues that still need ironing out:   - the semantics of keyword arguments have changed: you can no longer pass arbitrary keywords to a procedure and ignore those you are not expecting (on the other hand, unrecognised keywords are found at compile time);   - AFAIK, modules in the mzscheme language cannot call keyword procedures in modules written in scheme/base;   - also AFAIK, modules in scheme/base cannot call keyword procedures in mzscheme modules;   - the new style contracts from scheme/contract work fine with old style lambdas and opt-lambdas, but they do not work with lambda/kws;   - class.ss currently does not work correctly with either keyword system (I've filed a bug report about this one too). There are also some differences between the structure subforms in provide and provide/contract. If you provide a structure using provide/ contract, you cannot re-provide it using provide and struct-out. For example:   (module a scheme/base     (require scheme/contract)     (define-struct person (name) #:transparent)     (provide/contract (struct person ([name string?]))))   (module b scheme/base     (require (file "a.ss"))     (provide (struct-out person))) That's all I can think of for now. Cheers, -- Dave _________________________________________________  For list-related administrative tasks:  <a href="http://list.cs.brown.edu/mailman/listinfo/plt-scheme" target="_blank">http://list.cs.brown.edu/mailman/listinfo/plt-scheme</a> </blockquote></div>