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POYesod/Persistent testing with bracket pattern
 

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    <p>I'm very new to Haskell, so I'm having trouble absorbing all of the advanced features used in Yesod such as <a href="http://www.haskell.org/haskellwiki/GHC/Type_families#Instance_declarations_2" rel="nofollow">type instances</a> and <a href="http://www.haskell.org/haskellwiki/Type_families#Equality_constraints" rel="nofollow">equality constraints</a>. I am trying to implement the <a href="http://www.haskell.org/haskellwiki/Bracket_pattern" rel="nofollow">bracket pattern</a> in Yesod's test framework in order to get setUp/tearDown functionality. Here's what I've got so far (updated via edit):</p> <pre><code>module FishMother where import Control.Exception.Lifted import TestImport import Database.Persist import Database.Persist.GenericSql import Model insertYellowfinTuna :: OneSpec Connection FishId insertYellowfinTuna = runDB . insert $ Fish "Yellowfin Tuna" deleteFish :: FishId -&gt; OneSpec Connection () deleteFish = runDB . delete withYellowfinTuna :: FishId -&gt; OneSpec Connection () withYellowfinTuna = bracket insertYellowfinTuna deleteFish </code></pre> <p>The compile errors are as follows:</p> <pre><code>tests/FishMother.hs:18:21: Couldn't match type `FishId -&gt; Control.Monad.Trans.State.Lazy.StateT (Yesod.Test.OneSpecData Connection) IO ()' with `Key SqlPersist Fish' Expected type: FishId -&gt; OneSpec Connection () Actual type: (FishId -&gt; Control.Monad.Trans.State.Lazy.StateT (Yesod.Test.OneSpecData Connection) IO ()) -&gt; Control.Monad.Trans.State.Lazy.StateT (Yesod.Test.OneSpecData Connection) IO () In the return type of a call of `bracket' In the expression: bracket insertYellowfinTuna deleteFish In an equation for `withYellowfinTuna': withYellowfinTuna = bracket insertYellowfinTuna deleteFish </code></pre> <p>What am I doing wrong?</p>
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    1. USarussell84
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    1. COForget entirely about Yesod for the moment. If this was just normal `IO`, you'd have functions `setup :: IO FishId`, `tearDown :: FishId -> IO ()`, and then `withYellowfinTuna = bracket setup tearDown`. Play around with understanding what the type of that function would be first, and then come back to the Yesod world and try replacing `IO` with the `OneSpec Connection` monad.
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      1. USMichael Snoyman
    2. COThanks @michael-snoyman. Sometimes you just need to take a step back or even get some sleep in order to solve a problem. It also helped to know I was on the right track with `OneSpec Connection` and the types of the other functions. Here's the corrected type signature I was looking for: `withYellowfinTuna :: (FishId -> OneSpec Connection ()) -> OneSpec Connection ()`
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