The envelope package

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Dependencies aeson (>=0.11), base (>=4.8 && <5), http-api-data (>=0.3), mtl (>=2.2), text (>=1.2) [details]
License BSD3
Copyright 2016-2017 Dennis Gosnell
Author Dennis Gosnell
Category Web
Home page
Source repository head: git clone
Uploaded Wed Apr 19 06:24:15 UTC 2017 by cdepillabout
Distributions LTSHaskell:, NixOS:, Stackage:, Tumbleweed:
Downloads 331 total (16 in the last 30 days)
Rating 0.0 (0 ratings) [clear rating]
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Status Docs available [build log]
Last success reported on 2017-04-19 [all 1 reports]
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Readme for envelope-

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Build Status Hackage Stackage LTS Stackage Nightly BSD3 license

This module exports an Envelope type that can be used to wrap reponses from a JSON REST API. It provides a successful Success response, and a failure Err response.

Here is a small demonstration of returning a success response:

>>> import qualified Data.ByteString.Lazy.Char8 as C8
>>> import Data.Aeson (decode, encode)
>>> let successEnvelope = toSuccessEnvelope 3 :: Envelope Text Int
>>> C8.putStrLn $ encode successEnvelope
>>> decode "{\"data\":3}" :: Maybe (Envelope Text Int)
Just (EnvelopeSuccess (Success 3))

Your data gets wrapped in an object with a single "data" field:

    "data": 3

Now lets look at how an error response is encoded and decoded. It is encoded as an object with two members: @"extra"@ and @"error"@.

>>> let errorEnvelope = toErrEnvelope "DB_ERROR" "there was an error in the database" :: Envelope String Int
>>> C8.putStrLn $ encode errorEnvelope
{"extra":"there was an error in the database","error":"DB_ERROR"}
>>> decode "{\"extra\":\"there was an error in the database\",\"error\":\"DB_ERROR\"}" :: Maybe (Envelope String Int)
Just (EnvelopeErr (Err {errErr = "DB_ERROR", errExtra = Just "there was an error in the database"}))

Your error type and extra message get wrapped in an object:

    "extra": "there was an error in the database",
    "error": "DB_ERROR"