Can you just up-arrow/ctrl-r/m-p through your history?

@kulminaator source is implemented to look up the source file containing the code and extract it. it's not designed to find repl created fns

I have made this simple desktop wallpaper. Helps me keep focused on studying clojure. Enjoy!

I have a cljc file where I do #?(:cljs (:import goog.string.StringBuffer)) and then later use that as a replacement for StringBuilder. However, I have a type hint in the arguments box of a function where I send an instance of this. Like so:

(defn- foo [ast ^StringBuilder string-builder] ...

#?(:clj ^StringBuilder) should work I believe.

No, it won't, you can't use reader tags for metadata like that – you'll get a parse error about how the tag does not apply to anything (or something like that). You'd need to something like #?(:clj ^StringBuilder string-builder :cljs string-builder)

Howdy! Anyone ever built a duo out of a rust binary and a clojure uberjar? I’m interested how would one ship that into [canary] production [without Docker if possible].

@miikka, @dominicm: The first thing I tried was to just conditional the hint. That didn’t work and I ran out of ideas. 😃 The latter suggestion works great. Thanks!

Huh, I didn't realize that the metadata reader worked as a group not as an individual thing.

Yeah... It makes sense to me in the code-is-just-data sense but it's super annoying when you have to conditionally tag a lot of forms.

Which mechanism of polymorphism do you use most in UI? I tend to prefer multi methods, because they feel more natural, but maybe I get it wrong? I try to avoid giving functions as parameter in the rendering function, but am I mistaking?

(print-table [ {:a {:b 1 :c 2} :d 3} {:a {:b 4 :c 5} :d 6} ] [ [:a :c] :d] ) Result would be :a :c + :d +++++++++++++++ 2 + 3 5 + 6

is there any library that would do print-table with nested maps?

The original clojure.pprint/print-table does not like nested properties

I don't know the answer to your question. You may have already considered this, but you could write a function that creates a new map from your existing one, and then call print-table on that?

@andy.fingerhut Yes I am considering that.

In fact I am thinking of doing a pre-formatter

that adds nested properties

say I have :a {:b}

then I want to add a column :a-b

so the normal clojure print-table could be used,

and I only have to call (denest table) first.

The normal Clojure print-table might also work with a key of the form [:a :c] -- worth a test, anyway if the output from that meets your needs.

For example, the current print-table implementation can already do this:

user=> (pp/print-table [[:a :c] :d] [ {[:a :c] 2 :d 3}  {[:a :c] 5 :d 6}])

| [:a :c] | :d |
|---------+----|
|       2 |  3 |
|       5 |  6 |

As far as other 3rd party libs for printing tabular data, I am aware of these two, but not whether they already do what you want. You might want to scan the examples in their docs to check: https://github.com/cldwalker/table https://github.com/joegallo/doric

(clojure.pprint/print-table [:a [:c :d]]
    [ {:a 1 :b 2 :c {:d 3}}
      {:a 4 :b 5 :c {:d 6}} ]
           ) 

Wrote a lib recently to leverage spec for a looser form of multimethods. It's part idea-sketch, part pun, part maybe useful? See code examples in tests. https://github.com/den1k/defmostly

When using multimethods is it always required that an implementation namespace is required at some stage? I have a few multimethods which spread their defmethod implementations over several namespaces and I am finding (rather annoyingly) that these need to be required before use otherwise the dispatch clause simply will not be found. I haven't tried this in a running jar yet, only in testing/REPL but I am finding this to rather limit the openness/extensibility in that I need to be aware of the callpoints of the multimethod to make sure that the clause has been actually added to the system. Does the same happen when one compiles this down to an uberjar or is it enough then to simply require the namespace that holds the defmulti declaration?

you have to load the code to use the code

Thought as much. I wonder if given this it is better to simply place all the dispatch clauses in the same namespace as the multimethod declaration - that way, it's just one import away. How do folk usually do it here - single or multiple implementation namespaces for multimethods?

I don't use multimethods a ton, but in the past my conclusion was the way to structure things is as a diamond shape: namespace spi contains the defmulti, namespaces impl1 and impl2 require spi and contain defmethods, namespace interface requires impl1 and impl2 and defn's a wrapper around the defmulti

the diamond shape gives you a place to require all the implementations and also avoids circular dependency issues people stumble into with multimethods

depends on the use case. if you are using multimethods primarily to create a fixed set of polymorphic behaviors, then putting them all in the same place is easiest. if it's designed to be an open system, then it might make more sense to rely on some higher level of control to know how to declare the method and say which namespaces to load.

and agreed on the @hiredman's structure

What kind of higher level of control do you mean @alexmiller?

someone that is deciding what to load

either a fixed set of ns'es or possibly even an open set defined in config

I've done that with multimethods too, defining basically an interface as a group of multimethods and having some kind of config file that says which implementation of that interface to use and which namespace to load to get it

So either application specific (config.edn), or deriving implementation from keyword namespace (like integrant)?

I had considered using a data_readers.clj-like thing in the past too.

I think, for that kind of plugin thing I was doing then with multimethods, I would prefer a protocol now

Would be nice to have something in core, for libraries to load their extensions automatically if they're entirely about multi methods. But could be fixed in user space if library authors defining the multi methods could be brought on board.

Now that protocols can be attached to data, I also quite like the idea of using protocols.

multimethods and protocols both have the same issue of loading extensions, so I'm not sure it makes a difference

Some good tips here. True about protocols having the same issue, but that is typically something that I don't tend to hit as I tend to only have two implementations of any given protocol, but several dispatch clauses for a multimethod.

Hi. I'm trying to type hint a HashMap<String, byte[]>. How can I do that ? I'm doing this because Clojure's automatically picks the wrong static method (same method name, also accepts a HashMap, but with keys of a different type).

generics are mostly a fiction of javac, they only exist as an annotation in the bytecode, which most code never looks at

clojure type hints don't do generics at all

(they can hint ^HashMap but not the specialization)

can Java even do what you're describing? two methods that differ only in the generics?

can you point to public javadoc or anything?

yes you're right, my bad, they do differ by name, I guess I rushed and misinterpreted the error I got, sorry.

(if-let [{:keys [x y z]} {:not "what ~you~ i expect"}] "yep" "nope")

what do you expect this to do?

"nope"

i mean i sorta get it

but i repeatedly make the wrong assumption

maybe it makes sense if you think like (if-let [[x y] some-vector) vs (if-let [[x y] nil)

might help looking at macro expanded too:

(let*
  [temp__5718__auto__ {:not "what you expect"}]
  (if temp__5718__auto__
    (let*
      [map__64993
       temp__5718__auto__
       map__64993
       (if (clojure.core/seq? map__64993)
         (. clojure.lang.PersistentHashMap
          create
          (clojure.core/seq map__64993))
         map__64993)
       x
       (clojure.core/get map__64993 :x)
       y
       (clojure.core/get map__64993 :y)
       z
       (clojure.core/get map__64993 :z)]
      "yep")
    "nope"))

👼 if i'd find code that looks like that written by me i would just delete it and write it again ... (regarding that if-let from above)

too old to puzzle around complicated blocks

first 3 lines of the macro expansion say it all

anyway i must not be the only one because it was a pattern i found in code contributed to an open source project i maintain. fooled us both 🙂

rewritten:

(let [{:keys [x y z]} {:not "what you expect"}]
  (if (and x y z)
    "yep" "nope"))

What library would y'all recommend for HTML parsing?

Jsoup

Thanks! Works great