"Mastering Clojure Macros" by Colin Jones gets my vote as the go to book for writing clojure macros.
On Fri, Oct 2, 2015 at 8:24 AM, Colin Yates <colin.ya...@gmail.com> wrote: > Thanks for your comments - very helpful! > > The reference to destructuring might be irrelevant now. Previously I > noticed that the _map construction_ was emitted from the macro rather than > the symbol bound to the map. For example, some variation of quoting meant > (defmacro a [m] (println m)) called with (a {:1 1}) emitted (println {:1 > 1}) rather than (println m). Now I think about it is because an earlier > iteration of the macro used ~m - I’m not at the desk so I can’t confirm. > > Any pointers a decent Clojure macro book? I found lots of blogs around > from google but not a single one of them mentioned the (let [m-state > (gensym)] `(let [~m-state ~state])) ‘trick’. > > Thanks again. > > On 2 Oct 2015, at 10:50, gianluca torta <giato...@gmail.com> wrote: > > Hi Colin, > > as far as I can tell, your solution looks fine... here are a couple of > comments on your step-by-step analysis > > cheers, > Gianluca > > > 1(defmacro form [state & elements] >> 2 (let [m-state (gensym)] >> 3 `(let [~m-state ~state] >> 4 [:div.form.horizontal >> 5 ~@(map (fn [[f m & rest]] >> 6 `[~f (assoc ~m >> 7 :value (get @(:values ~m-state) (:id ~m)) >> 8 :on-change #(swap! (:values ~m-state) assoc >> (:id ~m) "UPDATED")) >> 9 ~@rest]) >> 10 elements)]))) >> >> 0 - ` means "emit, don't evaluate", ~@ means "splice, e.g. remove the >> outer sequence so [a ~@[1 2]] becomes [a 1 2] and ' means 'the symbol of >> rather than the value of'. >> > ~@ means "evaluate and splice", i.e., it overrides the "don't evaluate" of > ` and splices the result in the outer sequence > ~ means just "evaluate" without the splicing > > >> 2 - declare m-state, which is lexically scoped to the macro and is bound >> to a random identifier created by gensym >> 3 - the back-tick (syntax-quote) returns the form rather than evaluating >> the form, so the macro will return (let* [m-8_324230_ ....]) The [~m-state >> ~state] is just bewildering though. >> 3 - in addition, the 'state' argument appears to be destructured, but >> only to one level so if the state contains an atom it is the var of the atom >> > 'state' is evaluated due to ~, not sure what you mean by 'destructured, > but only to one level' > > >> 4 - literal text emitted in-line >> 5 - splice the results of the map (i.e. rather than [:div.form.horizontal >> [child1 child2]] return [:div.form.horizontal child1 child2]) >> 5 - also destructure each element assuming [f m(ap) and 0 or more other >> args] >> > yes, the destructuring is just a normal destructuring of the args passed > to the fn by map > > >> 6 - emit [<f> where <f> is the first symbol, 'f' l in each element. Also >> prevent this being evaluated in the macro with the syntax-quote as (5) has >> introduced some new scope because of the ~@ - not sure. >> > as said above, rather than introducing a new scope, ~@ just overrides the > "don't evaluate" of back-tick > > >> 6 - also associate onto the symbol m (which is assumed to be associative, >> e.g. a map)... >> 7/8 - extract data out of the 'run-time' (e.g. not macro-time) value of >> the provided state (magically captured under ~m-state) >> 9 - splice in the rest of the arguments, if any, that were part of the >> element >> 10 - and do that magic for each element >> > > > -- > 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. > -- You received this message because you are subscribed to the Google Groups "Clojure" group. 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