while( n > 1)
  tmp = a
  a = b
  b = tmp + b
  puts(b)
  n = n - 1
end
-- -- --
s(:list,  [s(:while, 
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    s(:operator,  ">", 
      s(:name,  "n"), 
      s(:int,  1))), 
  s(:expressions, 
    s(:assign, 
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      s(:name,  "a")), 
    s(:assign, 
      s(:name,  "a"), 
      s(:name,  "b")), 
    s(:assign, 
      s(:name,  "b"), 
      s(:operator,  "+", 
        s(:name,  "tmp"), 
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    s(:call, 
      s(:name,  "puts"), 
      s(:arguments, 
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    s(:assign, 
      s(:name,  "n"), 
      s(:operator,  "-", 
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        s(:int,  1)))))])