I'm glad my little library has gotten some attention on better-cond, which even I'm switching over to.
On Thu, Oct 4, 2018 at 10:39 PM Mark Engelberg <mark.engelb...@gmail.com> wrote: > Documentation for latest features in the 2.0.1 branch: > https://github.com/Engelberg/better-cond/tree/v2.0.1 > > An example: > > (cond > (odd? a) 1 > :let [a (quot a 2)] > :when-let [x (fn-which-may-return-nil a), > y (fn-which-may-return-nil (* 2 a))] > :when (seq x) > :do (println x) > (odd? (+ x y)) 2 > :else 3) > > The :do performs a side-effecting statement if it gets that far in the > cond. :do is my favorite bonus addition for cond beyond :let. I find I > use it a lot to quickly insert some debugging print commands without > needing to change the shape of my code, so it can be trivially removed > later. > > When :do did not exist, but :let did exist in my cond macro, I found > myself frequently writing things like: > :let [_ (println x)] > in order to insert a side-effecting statement into the cond sequence. > :do is a cleaner solution. > > :when only continues with the cond if the value is truthy, otherwise it > bails out of the cond with nil. > :when-some (not yet merged in) will do much the same thing, but continuing > if non-nil, rather than truthy. > > :when, :when-some, and :when-let don't add a whole lot of richness. For > example, that :when line in the example could just have easily been written > as: > (not (seq x)) nil > > But using these can potentially add clarity of intention, so even though I > could make do without them, I go ahead and use them when relevant. > > In better-cond's cond macro, that final :else is optional. You may prefer > the new cond-let library if you want to continue enforcing the use of :else > on the last clause. > > To reiterate, :let is by far the most valuable addition, and I find :do to > be the second-most valuable addition. Other additions are fairly minor > syntactic sugar. > > On Thu, Oct 4, 2018 at 1:36 PM Alan Thompson <clooj...@gmail.com> wrote: > >> How would the :when and :do forms work? >> Alan >> >> On Wed, Oct 3, 2018 at 7:22 PM Mark Engelberg <mark.engelb...@gmail.com> >> wrote: >> >>> This looks like a case of "convergent evolution". >>> >>> Having the ability to do a :let in the middle of a cond feels like one >>> of those things that *should* be in the core language, so if it's not >>> in there, a bunch of people are naturally going to arrive at the same >>> solution and make it happen in their own utility libraries. A bunch of us >>> Clojure programmers from the early 1.0 days had been privately passing >>> around and using a "cond that supports :let bindings" macro for years. The >>> first time I saw the macro was in a blog post by Christophe Grand. I really >>> hoped it would make it into Clojure proper -- other functional languages >>> like Racket and F# support ways to bind local variables with "clearer, more >>> linear code, that doesn't make a march for the right margin", as Howard >>> Lewis Ship put it. But after several years had passed without any >>> indication that CLJ-200 was ever going to be addressed, I eventually made >>> the improved cond macro into a clojars library. >>> >>> walmartlabs' cond-let addresses the most important thing (let), which is >>> the critical piece of functionality that feels like the most natural, >>> needed addition to the language. better-cond's :let syntax is identical. >>> But as us old-school Clojurians passed around the "better cond" macro over >>> the years, it grew in functionality. So in better-cond, I included the >>> other little improvements that had accumulated over time, which I had found >>> useful. So better-cond also supports :when, :when-let, and :do (and will >>> soon have :when-some). :let is the only piece that I felt really belonged >>> in the core language's cond, and if CLJ-200 had made it into the core >>> language, I would have been content to just use Clojure's own cond. But >>> once I realized I was going to need a library to achieve the much-needed >>> :let inside of cond, I figured I might as well use that library to include >>> the other convenient cond additions as well. So better-cond is a superset >>> of cond-let's functionality, with support for :let plus a few bonuses. >>> >>> Use whichever one strikes your fancy. cond-let is perfect if all you >>> care about is adding :let to your cond. If you want to experiment with >>> some of the other features beyond :let, you could use better-cond and see >>> what you think. >>> >>> Either way, I strongly encourage you to use one of these two libraries >>> so you can start using :let inside your cond. I agree fully with Howard >>> Lewis Ship that it results in clearer code. Try either library which >>> supports this -- it will change your life! >>> >>> >>> On Wed, Oct 3, 2018 at 5:05 PM Matching Socks <phill.w...@gmail.com> >>> wrote: >>> >>>> Is this a refinement of Mark Engelberg's "better-cond", or an >>>> alternative approach? >>>> >>>> I have not used better-cond myself, but it starts here: >>>> https://dev.clojure.org/jira/browse/CLJ-200. >>>> >>>> -- >>>> 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. >> 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. > -- Howard M. Lewis Ship Senior Mobile Developer at Walmart Labs (971) 678-5210 http://howardlewisship.com @hlship -- 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.
