T3395.hs:6:9:
    Illegal last statement of a list comprehension:
      r1 <- undefined
    (It should be an expression.)
    When splicing a TH expression: [r1 <- undefined | undefined]
    In the untyped splice:
      $(return
        $ CompE
            [NoBindS (VarE $ mkName "undefined"),
             BindS (VarP $ mkName "r1") (VarE $ mkName "undefined")])