How can I return something early from a block?

In this instance, you can use break to terminate the loop early:

collection.each do |i|
  break if i == 3
  ...many lines
end

...of course, this is assuming that you're not actually looking to return a value, just break out of the block.

#!/usr/bin/ruby

collection = [1, 2, 3, 4, 5 ]

stopped_at = collection.each do |i|
   break i if i == 3

   puts "Processed #{i}"
end

puts "Stopped at and did not process #{stopped_at}"

next inside a block returns from the block. break inside a block returns from the function that yielded to the block. For each this means that break exits the loop and next jumps to the next iteration of the loop (thus the names). You can return values with next value and break value.