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Comment by talideon | Hacker News Reader

Don't know Scala, but I'd assume that `+:` is prepend to list and `:+` is append to list.

You'd be correct.

But they're just method calls, both defined on the class of l. It is a little weird.

I can see the argument for terseness in source, particularly in domains where the terseness in code reflects well-understood shorthand in the actual problem space. But stuff like that makes me itch, to be honest.

The alternative would be something like

  l.prepend(a).append(b)

Horrible. Ghastly. Can't see anybody tolerating a language that looked like that.. /s

What? Mutating a list? DISGUSTING!

It's not mutating, its returning a new list with elements prepended and appended.

It gets even worse. Because Scala has infix syntax for method calls, you can do

    l prepend a append b

Don't know Scala but why wouldn't it be

a.append(l).append(b)

That would only work if a was itself a list..

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