Evail and binding - where are we going wrong?

Ruby
1 
# test_binding.rb

expression = "-> do  
	result = 1 + @x
	puts result
end"

test_lambda = -> { @x = 1  }

exp =  eval(expression, test_lambda.binding) 

exp.call

# I am expecting to see the result 2 being puts-ed to the screen.
# instead I'm seeing the following:

# (eval):2:in `+': nil can't be coerced into Integer (TypeError)
# 	from (eval):2:in `block in <main>'
# 	from test_binding_and_eval.rb:13:in `<main>'


# what am i doing wrong?

Any pointers would be appreciated?