On 02/17/2013 03:01 PM, Sergey Mironov wrote:
Hi folks. Hackage contains several JSON packages but as far as I see,
they all provide 'static' conversion from JSON format to Haskell data
type. Is there a method of converting object containing optional filed
'a' to for example Maybe a.
Assuming you have some sort of 'path' to the key in question, aeson-lens
might be exactly what you want:
http://hackage.haskell.org/package/aeson-lens
I use aeson-lens to turn a list of strings of the form ["foo", "bar",
"baz"] into a query into first the 'foo' object, then the 'bar' object,
then the 'baz' object, using the following:
pathToLens :: Functor f
=> [T.Text]
-> (Maybe Value -> f (Maybe Value))
-> Maybe Value
-> f (Maybe Value)
pathToLens [p] = key p
pathToLens ps = let ps' = filter (not . T.null) ps
in key (head ps') . (foldl (.) id . map pathElem $ tail
ps')
where
pathElem p = maybe (key p) nth (readMay $ T.unpack p)
So as you can see - I turn any arbitrary path into a query into JSON,
with a chance of failure.
Hope this helps!
- Ollie
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