The reason the "E_1" and the "e_1" are treated differently is that the "e" is mentioned in "binding" position of the shortcut. That is what makes it special. Does this make sense? (Have a read of the paragraph in the redex docs for reduction-semantics that talks about shortcuts and let me know if it makes more sense now and, even better, if you have any suggestions for edits!)
What if I were to actually make it do what people seem to think it does, in the case that the chosen name is a non-terminal? So, if you write a shortcut whose name is NOT a non-terminal, say "x" then it would be like you wrote "any_x". And if you used a non-terminal, then the shortcut would apply only when the expression actually matches the corresponding non-terminal. Redex would still have to insist that the parameters to the shortcuts are identifiers, but I could add in that restriction? This is also backwards incompatible, but in a different way, tho. So that's slightly worrying. This form of backwards incompatibility has the downside that it will just make things stop reducing instead of getting a syntax error. So we'd have to like it a LOT to go this way. Robby On Sun, Dec 20, 2015 at 2:44 AM, William J. Bowman <w...@williamjbowman.com> wrote: > I noticed this last week when I upgraded Redex for other reasons. It > broke one of my models, and I was momentarily confused. In fact, I > took the error message to mean I had somehow introduced an error and > spent some time staring at my tests to see if I had introduced a > syntax error. I only fixed the issue after investigating the git > commits to Redex. > > It is a little confusing that, in this one place (AFAIK), I have to > arbitrary names rather than non-terminal names. It is also strange > that my context non-terminal do not trigger this error. That is, with > non-terminals E and e defined, [(--> (in-hole E e_0) (in-hole E e_1)) > ...] triggers an error while [(--> (in-hole E e0) (in-hole E e1))] > does not; perhaps this is just my misunderstanding of how > reduction-relation works. > > -- > William J. Bowman > > On Sat, Dec 19, 2015 at 09:12:53AM -0600, Robby Findler wrote: >> I've recently pushed a change to Redex >> (https://github.com/racket/redex/commit/cbb2d88b) that disallows the >> names of non-terminals in shortcuts in reduction relations. I did this >> after seeing someone (quite reasonably!) assume that using a >> non-terminal there meant the shortcut would work only for terms >> matching those non-terminals, which is not how things actually work. >> >> The upside of making this an error is that, instead of having to study >> the minutiae of the reduction-relation-relation construct in the docs, >> Redex users are told when they think redex is fancier than it is in >> this respect. >> >> The downside is that this broke a bunch of old models I had lying >> around. I've fixed them (it's easy to do), but I worry that someone >> who gets out an old model to show it to someone will be greeted with >> this unexpected error message. >> >> Any opinions on whether or not I should revert this commit? >> >> Robby >> >> -- >> You received this message because you are subscribed to the Google Groups >> "Racket Users" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to racket-users+unsubscr...@googlegroups.com. >> For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
