[Haskell-beginners] Heterogenous list implemented with GADT

Ken Overton koverton at lab49.com
Thu Sep 30 15:08:01 EDT 2010

Hello fellow beginners (and the rest of you, too),  I was reading http://en.wikibooks.org/wiki/Haskell/GADT and I really liked the simple eval example.  But I reached the end and was confused by the following definition of a heterogenous list:

        data TG2 where
                MkTG2 :: Show b => [b] -> TG2

I had thought a heterogeneous list was something like

        [ 5 , 'Z', 3.14, False ]

How can the TG2 definition support the list I've given above?  Or am I just wrong about what a heterogeneous list is?


-- kov

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