let test_base: ('a, 'b, 'c) format = "GET&https%%3A%%2F%%2Fstream.twitter.com%%2F1.1%%2Fstatuses%%2Ffilter.json&oauth_consumer_key%%3Ddo944tkkUy4H6qJn49FVKpkQT%%26oauth_nonce%%3D%s%%26oauth_signature_method%%3DHMAC-SHA1%%26oauth_timestamp%%3D%s%%26oauth_token%%3D2649357145-b4gM74Eq8HaZ6W2ktPmTqjFXMvzAEhfKZ3mgfUT%%26oauth_version%%3D1.0%%26track%%3Dtwitter";;


Error: This expression has type
         (string -> string -> 'a, 'b, 'a) format =
           (string -> string -> 'a, 'b, 'a, 'a, 'a, 'a) format6
       but an expression was expected of type
         (string -> float -> 'c, unit, string) format =
           (string -> float -> 'c, unit, string, string, string, string)
           format6
       Type string is not compatible with type float