data-has: Simple extensible product

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Simple extensible product


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Versions 0.1.0.0, 0.2.0.0, 0.2.1.0, 0.3.0.0, 0.4.0.0, 0.4.0.0
Change log CHANGELOG
Dependencies base (>=4.8 && <5) [details]
License BSD-3-Clause
Author winterland1989
Maintainer winterland1989@gmail.com
Category Data
Home page https://github.com/winterland1989/data-has
Source repo head: git clone git://github.com/winterland1989/data-has.git
Uploaded by winterland at 2020-12-01T05:40:30Z

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Readme for data-has-0.4.0.0

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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 ...
       ...
...