The data-has package

[Tags:benchmark, bsd3, library]

Simple extensible product

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Change log CHANGELOG
Dependencies base (<5) [details]
License BSD3
Author winterland1989
Category Data
Home page
Source repository head: git clone git://
Uploaded Thu Nov 24 07:59:44 UTC 2016 by winterland
Distributions LTSHaskell:, NixOS:, Stackage:, Tumbleweed:
Downloads 89 total (12 in the last 30 days)
0 []
Status Docs available [build log]
Last success reported on 2016-11-24 [all 1 reports]




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Readme for data-has

Readme for data-has-


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A simple extensible product system, a typical usage is to free you from considering how to layer your monad stack, because your can now extend your monad in one layer:

 {-# LANGUAGE FlexibleContexts #-}

 -- in some library code
 logInAnyReaderHasLogger :: (Has Logger r, MonadReader r m) => LogString -> m ()
 logInAnyReaderHasLogger s = asks getter >>= logWithLogger s

 queryInAnyReaderHasSQL :: (Has SqlBackEnd r, MonadReader r m) => Query -> m a
 queryInAnyReaderHasSQL q = asks getter >>= queryWithSQL q

 -- now you want to use these effects together
 logger <- initLogger  ...
 sql <- initSqlBackEnd ...

 (`runReader` (logger, sql)) $ do
       logInAnyReaderHasLogger ...
       x <- queryInAnyReaderHasSQL ...