Arc Forumnew | comments | leaders | submitlogin
2 points by akkartik 2239 days ago | link | parent

Can you elaborate on what extra features Clojure's tables provide?


4 points by i4cu 2239 days ago | link

Where to start...

1. The ability to read them. Especially on output. It may seem small, but when you have a larger deeply nested map it really matters.

  {:user "akkartik"}
2. Keywords are ifns that work on hash-maps.

  (map :user list-of-maps)
3. All the built in library fns that work on them. Basics + Assoc-in, Get-in, merge, deep-merge, contains?..

Here's a good function to separate a collection of maps by any fn/ifn.

  (def separate (juxt filter remove))
 
  (separate :user data)
4. Iteration just works, ie they automatically become association lists for pretty much every composing fn (reduce, loop, ect)

5. Destructuring bind. Eg:

  (defn myfn [{:keys [user] :as record}]
    (str user " rocks"))
6. Nil values are supported.

It goes on, but I think that's enough... Besides my thumbs are getting sore typing via phone.

-----

3 points by akkartik 2239 days ago | link

You'll need to elaborate more, apologies in advance to your thumbs. Some of the features you describe I don't understand (ability to read, maybe others). Others seem to already be in Arc (library support, iteration, destructuring bind; [_ 'user] doesn't seem much worse than :user). Nil values feels like the only definitely missing feature, and it feels more like a fork in the road with different trade-offs rather than one alternative being always superior to the other.

-----

7 points by i4cu 2239 days ago | link

Ok so let's use this data

Clojure:

  > (def players
       {:joe {:class "Ranger" :score 100}
        :jane {:class "Knight" :weapon "Greatsword" :score 140}
        :ryan {:class "Wizard" :weapon "Mystic Staff" :score 150}})
response:

{:joe {:class "Ranger" :score 100} :jane {:class "Knight" :weapon "Greatsword" :score 140} :ryan {:class "Wizard" :weapon "Mystic Staff" :score 150}})

Arc:

  (= players
    (obj 'joe (obj 'class "Ranger" 'score 100)
         'jane  (obj 'class "Knight" 'weapon "Greatsword" 'score 140)
         'ryan  (obj 'class "Wizard" 'weapon "Mystic Staff" 'score 150)))
response:

#hash(((quote jane) . #hash(((quote weapon) . "Greatsword") ((quote class) . "Knight") ((quote score) . 140))) ((quote ryan) . #hash(((quote weapon) . "Mystic Staff") ((quote class) . "Wizard") ((quote score) . 150))) ((quote joe) . #hash(((quote class) . "Ranger") ((quote score) . 100))))

-- Readability --

Reading that output is beyond a headache. It should be against the law! But more importantly, when writing code/troubleshooting you can't copy the evaluated output make a modification and then call the function again. I know you can bind it and apply functions to modify it, but often that's a real hassle compared to copy/paste.

-- Destructuring bind --

See links [a,b]

I think simple cases don't show the difference.

  > (def book {:name "SICP" :details {:pages 657 :isbn-10 "0262011530"}})
  
  > (let [{name :name {pages :pages isbn-10 :isbn-10} :details} book]
      (println "name:" name "pages:" pages "isbn-10:" isbn-10))
response:

    name: SICP pages: 657 isbn-10: 0262011530
-- Library functions --

Clojure has DOZEN's of helper functions (and important traversal functions) that don't exist in Arc. Yeah I could write them, but I still have to. I was highlighting the ease with 'separate', but here's even 'deep-merge'....

  (defn deep-merge
    "Recursively merges maps. If keys are not maps, the last value wins."
    [& vals]
     (if (every? map? vals)
         (apply merge-with deep-merge vals)
         (last vals)))
		 
  > (deep-merge players {:joe {:weapon "LongBow"} :jane {:weapon "Lance"}})
It's not even these sample cases that expose the issues. It's about working with REAL data. I have many files containing hash-maps that are 15 levels deep. If I were to attempt pretty much anything, but the most simple cases, in Arc I would hit problem after problem after problem. Which I did. So fine... really I should use a DB, right? ok let me just grab that DB library in Arc....

-- Nil values --

I'd even be fine with any falsey values like boolean false. But Arc will not even store an #f value. To suggest I can't pass in REAL data with falsey values is really limiting. I can't pass in an options table argument. For every operation I would have to add more data or nuanced data or nuanced operations to support "this value was set, but it's set to 'NO' I don't want that option.".

[a] https://clojure.org/guides/destructuring#_associative_destru...

[b] https://clojure.org/guides/destructuring#_keyword_arguments

-----

3 points by akkartik 2239 days ago | link

Thanks! That's very helpful.

-----