haskell/aeson

JSON parsing with accumulative errors

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#578 opened on Aug 24, 2017

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 (8 comments) (1 reaction) (0 assignees)Haskell (1,298 stars) (334 forks)batch import
help wanted

Description

When parsing an incorrect JSON with Aeson, you only get the first error instead of all the errors like so:

Data.Aeson> eitherDecode "[1,19,\"a\", 20]" :: Either String [Text]
Left "Error in $[0]: expected Text, encountered Number"

It would be better to have another function to return all the errors instead of just the first one, for example:

Data.Aeson> eitherDecode "[1,19,\"a\", 20]" :: Either [(String, String)] [Text]
Left [("$[0]", "Expected Text, encountered Number"), ("$[1]", "Expected Text, encountered Number"), ("$[3]", "Expected Text, encountered Number")]

This kind of feature would be very useful in web development where errors in request payload are all checked at once to save network round trip.

I'm thinking maybe this library can be used instead of Either https://hackage.haskell.org/package/Validation-0.2.0/docs/Data-Validation.html

Contributor guide

Tech stack
None
Domain
backenddeveloper experience
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Haskell programmingAeson libraryJSON parsing
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50
Research direction
Investigate the current error handling in Aeson's parser, likely in Data/Aeson/Types.hs or Data/Aeson/Parser.hs. Review the issue comments for additional discussion on implementation approach. Consider using a Validation type to accumulate errors as suggested in the issue. Look at existing functions like 'eitherDecode' and 'eitherDecodeWith' to understand the current error reporting mechanism.
JSON parsing with accumulative errors · haskell/aeson#578 | Good First Issue