How do ambigious types compile with Aeson

13 Sep 2015

      Hi list,
...
ghci> decode $ fromStrict $ encodeUtf8 $ "{\"a\" : \"b\"}"
Nothing
...
ghci> decode $ fromStrict $ encodeUtf8 $ "{\"a\" : \"b\"}" :: Maybe Object
Just (fromList [("a",String "b")])
The question is: how can the first example compile? I would expect that
since GHC cannot infer the type I want from Aeson to decode to, it would
die with an error that "t0 type variable is ambigious". But instead, it
compiles just fine, and fails runtime.

How it's decided what type should Aeson try to decode to? What type is that
gives me Nothing on whatever JSON input I give?

Cheers,
Andras Sevcsik

-- 
Minden jót,
Sevcsik András

Sevcsik András

Brandon Allbery

Sevcsik András

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