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 <[email protected]> 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 [email protected]. >> 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 [email protected]. For more options, visit https://groups.google.com/d/optout.
