# Need help to understand how ghc loads the plugins

**URL:** <https://discourse.haskell.org/t/need-help-to-understand-how-ghc-loads-the-plugins/6122>\
**Category:** Learn\
**Created:** [April 9, 2023, 8:43am UTC](https://discourse.haskell.org/t/need-help-to-understand-how-ghc-loads-the-plugins/6122 "2023-04-09T08:43:40Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![AravindGopal](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.haskell.org/aravindgopal/32/2068_2.png) [@AravindGopal](https://discourse.haskell.org/u/AravindGopal)\
**Post date:** [April 9, 2023, 8:43am UTC](https://discourse.haskell.org/t/need-help-to-understand-how-ghc-loads-the-plugins/6122/1 "2023-04-09T08:43:40Z")

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Please help to understand how compiler load the plugins. trying to implement a tool using GHC as library, where it’s not loading the plugins. Modified `parseModule` function to call `initializePlugins` which resolved the source but failing on typecheck. Any help would be appreciated.

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**Author:** ![AravindGopal](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.haskell.org/aravindgopal/32/2068_2.png) [@AravindGopal](https://discourse.haskell.org/u/AravindGopal)\
**Post date:** [April 10, 2023, 6:48pm UTC](https://discourse.haskell.org/t/need-help-to-understand-how-ghc-loads-the-plugins/6122/2 "2023-04-10T18:48:04Z")

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Can anyone help in understanding the flow of how plugins are introduced on each step of GHC (8.8.4) pipeline.

Our use case is `cabal build` is working fine. But when the same code is tried to be parsed with `GHC library` the plugin is not being initialised.

Any help would be appreciated! Thanks

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<div class="post-metadata">

**Author:** ![AravindGopal](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.haskell.org/aravindgopal/32/2068_2.png) [@AravindGopal](https://discourse.haskell.org/u/AravindGopal)\
**Post date:** [April 10, 2023, 7:11pm UTC](https://discourse.haskell.org/t/need-help-to-understand-how-ghc-loads-the-plugins/6122/3 "2023-04-10T19:11:54Z")

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> <https://github.com/google/haskell-indexer/issues/93>
>
> ghc-8.6, when using the GHC API, requires that plugins be initialized explicitly… for each module. (Previous versions of the API initialized them automatically).
> See for example:
> https://github.com/sol/doctest/pull/224
> 
> The following file that uses \`ghc-typelits-knownnat\` can reproduce the problem. It builds fine with ghc-8.6, but fails to load in the indexer. I applied a patch on our internal codebase similar to the above doctest PR, but wasn't sure how to test it in this codebase given the external dependency requirement.
> 
> \`\`\`
> {-# OPTIONS\_GHC -fplugin=GHC.TypeLits.KnownNat.Solver #-}
> {-# LANGUAGE DataKinds #-}
> {-# LANGUAGE ScopedTypeVariables #-}
> {-# LANGUAGE TypeOperators #-}
> module Main (main) where
> 
> import Control.Exception (assert)
> import Data.Proxy
> import GHC.TypeLits
> 
> \-- | Requires ghc-typelits-knownnat to solve its constraints:
> plusOne :: forall n . KnownNat n =\> Proxy n -\> Integer
> plusOne \_ = natVal (Proxy :: Proxy (n + 1))
> 
> two :: Integer
> two = plusOne (Proxy :: Proxy 1)
> 
> main :: IO ()
> main = assert (2 == two) $ return ()
> \`\`\`

The above issue helped. Tried it, it’s working now.