On Sun, Dec 20, 2015 at 08:42:25PM -0600, Robby Findler wrote: > 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? Yes, thank you.
> (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!) I read through the documentation at http://pkg-build.racket-lang.org/doc/redex/The_Redex_Reference.html?q=reduction-relation#(mod-path._redex/reduction-semantics). The closest paragraph I can see to talking about this seems out of date. "Each shortcut clause defines arrow names in terms of base-arrow-name and earlier shortcut definitions. The left- and right-hand sides of a shortcut definition are identifiers, not patterns and terms. These identifiers need not correspond to non-terminals in language." Of course now, the last sentence requires s/need not/must not/. I would also add a final sentence such as "Therefore, the output of the shortcut is not checked against the syntax of any non-terminal." > 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. The fact that it will cause previously good code to fail silently is rather unacceptable. Although, I think this changed behavior is preferable because it matches the behavior of much of the rest of Redex, and matches what people seem to except. Perhaps a different syntax for this changed version of shortcut, and deprecating the current version? -- William J. Bowman -- 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.
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