As a counterpoint to this, note that ClojureScript does the same thing (for different reasons, but the same mechanism):
https://github.com/clojure/clojurescript/blob/master/src/main/clojure/cljs/core.cljc#L91-L101 On 1 January 2017 at 05:24, Timothy Baldridge <tbaldri...@gmail.com> wrote: > Be really careful with Potemkin. I've had a lot of build issues > (especially around AOT) with that library. I'll try to put this as kindly > as I can...it's a bit of a hack that leverages some undocumented aspects of > the Clojure API. As such it's been the source of some really weird compile > errors that have taken me many hours to debug. So much so that some > libraries have go so far as to copy-paste certain files from potemkin > (macros around map-like type creation), in order not to get the more > fragile parts of the library (var reorganization). > > In short...the language wasn't designed to do what Potemkin tries to make > it do when it comes to vars. I really recommend against using the library. > > On Sat, Dec 31, 2016 at 7:32 AM, squeegee <squee...@mac.com> wrote: > >> >> >> On Friday, December 30, 2016 at 8:59:46 PM UTC-5, puzzler wrote: >>> >>> On Fri, Dec 30, 2016 at 4:55 PM, Timothy Baldridge <tbald...@gmail.com> >>> wrote: >>> >>>> I can see that, and even spec has this use case. In Spec it's solved by >>>> having both A and B in one namespace and using declare to forward-declare >>>> the constructors (or defns in this case). >>>> >>>> So I guess the way I see it the tradeoff is a declare and >>>> all-in-one-namespace vs a massive complexity addition to the compiler and >>>> the redefinition of compilation units. The declare method seems like the >>>> cleaner route. >>>> >>>> >>> I wonder whether there could be something like an `external-declare` >>> that would satisfy Rich's concerns about knowing how to intern >>> unencountered vars, while allowing cyclical references when needed. >>> >> >> The macros defined in ‘scarlett.core’ here: https://github.com/scgil >> ardi/scarlett are an experiment along those lines. >> >> *scarlett* >> >> Provides macros to declare vars in namespaces other than *ns* >> >> To be used sparingly to overcome otherwise cyclic namespace dependencies >> >> *Usage* >> >> (ns-declare my-module startup shutdown) >> >> declares my-module/startup and my-module/shutdown >> >> (declare+ module-a/startup module-b/startup) >> >> declares module-a/startup and module-b/startup >> >> >> They work by using “declare” after switching to the target namespace >> using “in-ns” (and switching back at the end). They have to be issued at >> the “top level” (as is highly recommended for ns, declare, def, etc.) to be >> effective and they contain code to notify with an exception if they are >> used at other than the top level. (The exception is preferable to silent >> failure or a confusing error message.) >> >> >> The macros rely on the compiler behavior of handling top-level “do” forms >> in a special way: evaluating each of the contained forms sequentially *at >> the top level*, effectively removing the nesting and allowing each >> contained form to be compiled and evaluated before compiling the next one. >> Macro expansion facilities other than the compiler (e.g., in an editor or >> debugger) may not duplicate that subtle behavior so the expansions they >> produce may not accurately reflect the expansion that will be produced and >> seen by the compiler. There may be contexts where that causes trouble at >> development time. >> >> >> I’m not aware of these being used anywhere in other than experimental/POC >> code. >> >> >> —Steve >> >> -- >> 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. >> > > > > -- > “One of the main causes of the fall of the Roman Empire was that–lacking > zero–they had no way to indicate successful termination of their C > programs.” > (Robert Firth) > > -- > 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.
