Proposal for how to handle sequences of pairs where left/right don't fit on one line.

[kkinnear]

One of the differences in Clojure from other Lisps that I have used is that frequently there are pairs of s-expressions without enclosing parentheses. These show up in binding vectors in let,when,if-let and their relatives. These pairs also show up in assoc, cond, condp, and case.

I like this syntactic clarity, but when writing code with other than single character local names in let, and with expressions for assoc, sometimes the pairs don't fit on the same line. In this case, the default approach is to simply place them all in line on the left. I find this difficult to read.

I have taken to indenting what would be the right-hand side of the pair (if it were on the same line) by 2 spaces so that the left-right relationship remains clear even if the two "sides" are on different lines.

; default approach
(let [local-value1 (expr1)
      another-value (expr2)
      third-value 
      (a (very (long (expression (that (doesnt (fit on) one line))))))
      result-of-the-long-expression
      (another (expression (that (is too long) for one) line))]
  (result-of-the-long-expression))

; a possibly better alternative
(let [local-value1 (expr1)
      another-value (expr2)
      third-value 
        (a (very (long (expression (that (doesnt (fit on) one line))))))
      result-of-the-long-expression
        (another (expression (that (is too long) for one) line))]
  (result-of-the-long-expression))

I have not seen anyone else do this, so I certainly can't say that this is idiomatic Clojure. However, I wanted to bring it up for discussion and consideration.

Of course, one approach is to not let this happen. But at least in my code, I sometimes have rather complex expressions on the right hand side of let binding vectors, as well as on both sides of assoc pair lists. To say nothing of cond and friends.

[uvtc]

Is this a common enough ocurrence that it would need to go into the style guide?

Perhaps if your let binding values are too long, you could instead break them up into more intermediate values?

[CampingScorpion]

@kkinnear I too hate seeing the default approach. In this case I usually just go over 80 lines (which I don't hink is such a big deal). I think your proposal would be a good one if we had the power to change the way lisp code got layed out across the community, but I doubt that is likely.

[ToBeReplaced]

I like the idea, though it would be particularly tricky for editors since there is no way to distinguish between "this is a list of independent elements" and "this is a list of pairs of elements". I think that the proposal might be more appropriate for maps?

Instead of the default, I currently do this, and I know it's ugly :).

(let [local-value1 (expr1)
      another-value (expr2)
      third-value (a (very (long (expression 
                                   (that (doesnt (fit on) one line))))))
      result-of-the-long-expression (another (expression 
                                               (that (is too long) for one) line))]
  (result-of-the-long-expression))