I am not a rubyist, but a block (which I think is properly called a proc) is different from a regular lambda in that its control flow statements are lexically s

I am not a rubyist, but a block (which I think is properly called a proc) is different from a regular lambda in that its control flow statements are lexically scoped to the method it is defined in. A return statement in a lambda returns from a lambda (and always succeeds), a return statement in a block returns from the method the block was defined in (and fails with a LocalJumpError if the call frame is no longer on the call stack). I think Kotlin has a similar distinction between lambda expressions that return from the definer (and it ensures that you're passing them to an inline function that won't save the closures for later) and anonymous functions that return from themselves.