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Comment by rlander | Hacker News Reader

You’re missing the crux of the argument: auto-currying. In languages like Elm and Ocaml all functions are single arity which means a multi-arity function is just a partially-applied single arity function thus you can treat all functions as being single arity. This also means the pipe operator can be implemented as a higher order function being, as such, first class. Languages without auto-currying have to resort to macros.

Clojure also doesn’t have auto currrying, but makes up for it by giving you 6 variants and creating a consistent default library for sequences and associative structures.

So, the pipe first operator is just a dirty hack.

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I'm familiar with auto-currying from Haskell I've never worked seriously in a language that has it. But yes, that makes sense! I never thought about that.

I'm a bit stuck on your Clojure example still, though. If a language doesn't have auto-currying (or even currying at all in Elixir's case), why does the argument order matter? Whether it's a List or a Map, what does it matter if it's passed first instead of last?

There is no general implicit currying. I suppose if we are exact with CS terminology, currying means converting to 1-argument functions, so that's out.

But the threading macros do partial application in that they put the threaded-through value as an implicit argument. Look at the first examples in https://clojure.org/guides/threading_macros - the -> (thread-first) macro needs functions like assoc and update to take the map as the first argument.

And of course explicit use of partial application is also pretty common and argument order matters similarly there, just like it would eg in Python.

I was more after an example of why argument order matters in currying collection functions, but I actually get it now :) With the object as the last parameter, you are able to create a function that, say, always reduces to a list with a specific function and takes an object. So yes, I understand peoples' objections now.

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