I don't understand why Smalltalk doesn't allow me to have an or:
method that takes a block argument (except on Boolean). For example:

Set or: 1. ==> MNU as expected.

Set or: [1]. ==> NonBooleanReceiver exception.

Set or: [:x | x] ==> Argument has too many arguments

Is it because the compiler specializes this to boolean when it sees
the or: [ ... ] syntax? Is this a tradeoff made for performance?

greetings,
  Lorenz