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Improve generic decoding errors #10

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Merged
merged 1 commit into from
Jan 13, 2016
Merged

Improve generic decoding errors #10

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9 changes: 5 additions & 4 deletions src/Data/Argonaut/Decode.purs
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Original file line number Diff line number Diff line change
Expand Up @@ -51,13 +51,14 @@ gDecodeJson' signature json = case signature of
sp <- gDecodeJson' (val unit) pf
pure { recLabel: lbl, recValue: const sp }
SigProd typeConstr alts -> do
let decodingErr msg = "When decoding " ++ typeConstr ++ " " ++ msg
let decodingErr msg = "When decoding a " ++ typeConstr ++ ": " ++ msg
jObj <- mFail (decodingErr "expected an object") (toObject json)
tag <- mFail (decodingErr "'tag' string property is missing") (toString =<< M.lookup "tag" jObj)
tagJson <- mFail (decodingErr "'tag' property is missing") (M.lookup "tag" jObj)
tag <- mFail (decodingErr "'tag' property is not a string") (toString tagJson)
case find ((tag ==) <<< _.sigConstructor) alts of
Nothing -> Left ("'" <> tag <> "' isn't a valid constructor")
Nothing -> Left (decodingErr ("'" <> tag <> "' isn't a valid constructor"))
Just { sigValues: sigValues } -> do
vals <- mFail "'values' array is missing" (toArray =<< M.lookup "values" jObj)
vals <- mFail (decodingErr "'values' array is missing") (toArray =<< M.lookup "values" jObj)
sps <- zipWithA (\k -> gDecodeJson' (k unit)) sigValues vals
pure (SProd tag (const <$> sps))
where
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