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Comment by agumonkey | Hacker News Reader

How large are these s-exp ? Lisp is unreadable when nested too much (I'm starring at an xml->s-exp dump and I don't even wanna try to read it), but usually lisp code and data tend to be factored into little combinators and separated specific functions. If you can, try to split them.

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Here's a link to an example of that coping strategy from some bad Clojure I wrote last night [1]. I sometimes use an accumulation of lets for a similar effect, but only when describing simpler transformations.

The lets might look like so (warning- silly example):

    (defn n-squared-over-two-plus-three-as-str [n]
      (let [squared (* n n)
            halved  (/ squared 2.0)
            added   (+ halved 3)]
        (str added)))
     
    > (n-squared-over-two-plus-three-as-str 1)
    "3.5"

Sure, I could've just done this as a deeply-nested structure:

    > ((fn [n] (str (+ 3 (#(/ % 2.0) (* n n))))) 1)
    "3.5"

... but it's harder to read, debug, and reason about. You wouldn't do that in a non-functional language either! I suppose the tolerance for deep nesting is different for different programmers.

[1] https://github.com/dpritchett/cloball/blob/62300d31666ab1261...

Thanks for the edition, the code wasn't as obvious. I believe Haskell `where` construct is to write code this way (beside the flipped order).

That looks like a good place to use the arrow macro http://clojuredocs.org/clojure_core/clojure.core/-%3E

Yep, that's what the link in my original post was hoping to demonstrate. I find rolling up a few lets one after the other more natural in some other situations.

Although I'm second-guessing my let example now. Lets are great for assigning names to your building blocks, but I don't really like using them to obscure my processing flow as above. Perhaps this would be a better compromise:

    (defn example [n]
      (let [square #(* % %)
            halve  #(/ % 2.0)
            add3   #(+ % 3)]
        (-> n square halve add3 str)))
    
    > (example 1)
    "3.5"

If the function name or docstring is descriptive enough, I'd just go for

    (defn square-halve-add3-to-string [n] 
      (-> n 
        (#(* % %)) 
        (/ 2.0) 
        (+ 3) 
        str))

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