makePropertyObj code does not work and left undefined, 13.3. USING GENERIC METADATA, page 183 #33
Description
Hi,
I tried the code for makePropertyObj at 13.3. USING GENERIC METADATA, page 183
it gives type error. Also checked the code on github it is left as undefined
the original code is (shown as on the book)
makePropertyObj :: forall name . (KnownSymbol name) => Value -> Value
makePropertyObj v = object [pack (symbolVal $ Proxy @name) .= v ]
I noticed the error was due to Haskell could not infer the type as Key from the code pack (symbolVal $ Proxy @name) and was giving below error (which worked for makeTypeObj function)
• Couldn't match expected type ‘Key’ with actual type ‘Text’
• In the first argument of ‘(.=)’, namely
‘pack (symbolVal $ Proxy @name)’
In the expression: pack (symbolVal $ Proxy @name) .= v
In the first argument of ‘object’, namely
‘[pack (symbolVal $ Proxy @name) .= v]’typecheck(-Wdeferred-type-errors)
I made some small changes and Key to import list from aeson package also used fromText and imported Data.Aeson.Key (fromText) and used fromText to convert Text to key and it works i believe if it is the intent;
here is the slightly modified code;
makePropertObj :: forall name . KnownSymbol name => Value -> Value
makePropertObj v = object [fromText (pack (symbolVal $ Proxy @name)) .= v ]
and just did a quick check on it if it works as it is
-- >>>makePropertObj @"age" (makeTypeObject @Int)
-- Object (fromList [("age",Object (fromList [("type",String "integer")]))])
also the changes on the import list I made ;
import Data.Aeson (Value (..), (.=), object, Key)
import Data.Aeson.Key (fromText)