Yep, I spent some time playing with the macro and the macroexpand. It looks like
a) it only works if the dependent keys come *before* the keys they depend on (ie the opposite of how you'd order, say, defs) b) this ordering arises entirely from the seq ordering of PersistentArrayMap (keys are stuck into the map here https://github.com/clojure/clojure/blob/clojure-1.6.0/src/clj/clojure/core.clj#L4083 and taken out again here https://github.com/clojure/clojure/blob/clojure-1.6.0/src/clj/clojure/core.clj#L4090 ) The latter makes it pretty clear that this is accidental behavior and, as you say, shouldn't be relied on -- in particular, if you have more than about 8 keys, you spill over to a PersistentHashMap and get everything in a random order and it almost certainly fails. The trouble is this behavior is already used by ring-middleware-format, which then fails to compile if clojure uses a different implementation for small maps. I'm wondering if given the brittleness of this behavior we should make sure it can't be used in future versions of clojure. On Thu Dec 11 2014 at 6:56:22 PM <adrian.med...@mail.yu.edu> wrote: > Whenever you want to get insight in how a macro is rewriting your code, > try evaluating your form quoted with macroexpand. > > Here's a gist with the macroexpansion each form. > > https://gist.github.com/aamedina/542b084d31d4e0c9a7a8 > > Hopefully the expansion makes things clear! > > On Thursday, December 11, 2014 6:11:59 PM UTC-5, Michael Blume wrote: >> >> If I make my defaults on a :keys :or destructuring depend on the values >> of other keys, I *can* get a compile-time error, depending on what order I >> give the keys https://gist.github.com/MichaelBlume/4891dafdd31f0dcbc727 >> >> Is this on-spec behavior? Should the former be allowed but not the >> latter? Should both be allowed? Should neither? >> > -- > You received this message because you are subscribed to the Google > Groups "Clojure" group. > To post to this group, send email to clojure@googlegroups.com > Note that posts from new members are moderated - please be patient with > your first post. > To unsubscribe from this group, send email to > clojure+unsubscr...@googlegroups.com > For more options, visit this group at > http://groups.google.com/group/clojure?hl=en > --- > You received this message because you are subscribed to the Google Groups > "Clojure" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to clojure+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 "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
