The square brackets are used already for type parameters on types. I do think they are easier to read than angle brackets are, for some reason. There was some d

The square brackets are used already for type parameters on types. I do think they are easier to read than angle brackets are, for some reason. There was some discussion on this point in the Rust community as well recently where it was noted several people found square brackets easier to read and wanted to emulate Scala here (and another group wanting emulate D, using () for both!). Another reason is that an IndexedSeq is really itself a function (extends Function1), so the parens are literally function application, not some specially interpreted syntax for indexing.