Ruby code doesn't work when encapsulated in function

Question

I'm trying to access kinesis from ruby. I have very very little experience with ruby. I wrote some code in REPL (shell). The code works great, but for some reason, when I wrap it in a function, it doesn't work as expected. Why?

➜  ~  pry
# some definitions
[1] pry(main)> @AWS_ACCESS_KEY_ID='SOMETHING'
=> "SOMETHING"

[2] pry(main)> @AWS_SECRET_ACCESS_KEY='SECRET'
=> "SECRET"

[3] pry(main)> require 'aws-sdk'
=> true

[4] pry(main)> @limit = 100
=> 100

[5] pry(main)> Aws.config.update({region: 'us-east-1', credentials: Aws::Credentials.new(@AWS_ACCESS_KEY_ID,@AWS_SECRET_ACCESS_KEY)})
=> {:region=>"us-east-1", :credentials=>#<Aws::Credentials access_key_id="SOMETHING">}

[6] pry(main)> @kinesis = Aws::Kinesis::Client.new()
=> #<Aws::Kinesis::Client>

# bar gets a list of all streams
[7] pry(main)> def bar
[7] pry(main)*   @kinesis.list_streams.stream_names
[7] pry(main)* end
# bar seems to work!
=> :bar

[8] pry(main)> bar
=> ["mystream", "my.other.stream"]

[9] pry(main)> @stream = "my.other.stream"
=> "my.other.stream"

# foo gets elements from the stream
[11] pry(main)> def foo
[11] pry(main)*   puts @stream
[11] pry(main)*   puts @limit
[11] pry(main)*   @iter = @kinesis.get_shard_iterator(stream_name: @stream, shard_id: '0', shard_iterator_type: 'LATEST')
[11] pry(main)*   @kinesis.get_records(shard_iterator: @iter.shard_iterator, limit: @limit).records.map {|x| x.data}
[11] pry(main)* end
=> :foo

# it can see vars like @limit and @stream, but it retunrs an empty list
[12] pry(main)> foo
my.other.stream
100
=> []

# this is the size of the list:
[15] pry(main)> foo.length
my.other.stream
100
=> 0

# now let's do the same as foo, but not in a function: we get size 11
[18] pry(main)> @iter2 = @kinesis.get_shard_iterator(stream_name: @stream, shard_id: '0', shard_iterator_type: 'LATEST')
=> #<struct Aws::Kinesis::Types::GetShardIteratorOutput
 shard_iterator=
  "AAAAAAAAAAEt2rBZY0E8eaBQgJ2sy/se4OL0VaGI6AAAAAAAAAAEt2rBZY0E8eaBQgJ2sy7A+sqE3udpLF5hQIXokaKzo8fGV4o+dpLF5hQIXokaKzo8fG+m/GJrerouDlzpr8k7CLUYT53FzOpRJdpLF5hQIXokaKzo8fGfsux80pQaGMpIpqwHw3/fvAoKyR4RhzaIQzHIBoklHf">

[19] pry(main)> (@kinesis.get_records(shard_iterator: @iter2.shard_iterator, limit: @limit).records.map {|x| x.data}).length
=> 11