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Comment by Chris_Newton | Hacker News Reader

To be fair, comparing something like this:

    (partition-by #(> % 60) [49 58 76 82 88 90])

to so-called line noise code seems reasonable enough. As with Perl, if you immediately know what all the punctuation means and what the underlying structure of the language is, it’s concise, but if you don’t, it’s quite a mess of random-looking symbols.

For comparison, here’s a Haskell version, which in this case has a more intuitive syntax, IMHO:

    filter (>60) [49, 58, 76, 82, 88, 90]

And here’s a version in Scala, with a more explicit function value:

    List(49, 58, 76, 82, 88, 90).filter(n => n > 60)

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Really? There's only two bits of punctuation there, and they don't take much to explain: #(...) is an anonymous function; % is the argument to that function. (I'm not counting > because ... it's just the greater-than sign.)

The Haskell version doesn't actually do the same thing. The Haskell returns [76, 82, 88, 90]; the Clojure returns ((49 58) (76 82 88 90))---it groups the input according to the result of the function, it doesn't just filter it.

It’s not an ideal example of partition-by anyway, because this particular input has all the values where the predicate returns true together. As you have shown, the result in this case is just to divide the list into the values that match the predicate and those that don’t. This is actually what the “partition” function does in some languages, including Haskell and Scala. However, in general, partition-by in Clojure does more than that and is more like a kind of split algorithm, which this example didn’t demonstrate.

In any case, my point here was about syntax, so I used a standard and easily recognisable function in the other languages instead of getting bogged down in trying to reproduce the exact same behaviour. Apologies if this wasn’t clear.

I know this is a discussion on syntax but I can't help pointing out that the semantics of paritition-by and filter are very different.

True enough, but I figured filter was widely known and partition-by was perhaps a little esoteric. The syntactic argument would be exactly the same if you used an equivalent of partition-by in the other languages.

>(partition-by #(> % 60) [49 58 76 82 88 90])

Yeah, a less noisy way to do it in Clojure would be

(partition-by (partial < 60) [49 58 76 82 88 90])

You are right.

in Perl:

grep { $_ > 60 } ( 49, 58, 76, 82, 88, 90)

Scala : List(49, 58, 76, 82, 88, 90).filter( _ > 60 )

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