Improve message produced by eitherResult for Partial #207
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chris-martin
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Is this change okay? Is there anything I can do to improve it? |
bgamari
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Apr 29, 2022
Data/Attoparsec/ByteString.hs
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| T.Done _ r -> Right r | ||
| T.Fail _ [] msg -> Left msg | ||
| T.Fail _ ctxs msg -> Left (intercalate " > " ctxs ++ ": " ++ msg) | ||
| T.Partial _ -> error "feed result mempty = Partial _" |
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This seems like a less understandable error than the original. Perhaps something like "eitherResult: Partial" would be less ambiguous?
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I don't mind changing it, but just to make sure we're on the same page - this is not a substitute for the error message that was previously returned when the parse result was partial. This is an error message that will never be seen.
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When a parser result is Partial, previously the eitherResult function
showed a generic error message that includes no useful information other
than a generic "incomplete input" message.
For example, if we let
p = (,) <$> letter <*> digit <?> "thing"
then
eitherResult (parse p "a") = Left "Result: incomplete input"
Attoparsec is already capable of generating more informative error
information for this example, as we can demonstrate by using parseOnly:
parseOnly p "a" = "thing > digit: not enough input"
This change brings that same error message to eitherResult by simply
feeding `mempty` into the continuation. With this change, eitherResult
now gives the same output as parseOnly.
eitherResult (parse p "a") = "thing > digit: not enough input"
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When a parser result is
Partial, previously theeitherResultfunction showed a generic error message that includes no useful information other than a generic "incomplete input" message.For example, if we let
then
Attoparsec is already capable of generating more informative error information for this example, as we can demonstrate by using
parseOnly:This change brings that same error message to
eitherResultby simply feedingmemptyinto the continuation. With this change,eitherResultnow gives the same output asparseOnly.