Chris Biscardi

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GHC -ddump-minimal-imports and CPP error: missing binary operator before token "("

Today I was trying to extract the minimal imports for a module using ghc -ddump-minimal-imports but I was getting this error on some files:

error: missing binary operator before token "("
#if MIN_VERSION_base(4,4,0)

Which is related to the fact that cabal expands MIN_VERSION_base macros when running cabal build, so we don’t have them when running ghc or ghci. Luckily it’s an easy fix.

Cabal generates a macros file relative to the root of the project at dist/build/autogen/cabal_macros.h. We can include this file to gain access to the macros:

ghc -ddump-minimal-imports -optP-include -optPdist/build/autogen/cabal_macros.h src/Types.hs

Which will now spit out our imports into a file called Types.imports and may look something like this:

import Blaze.ByteString.Builder
( Builder, fromLazyByteString, fromByteString )
import Blaze.ByteString.Builder.Char.Utf8
( fromText, fromLazyText )
import Control.Applicative
( Applicative((), pure), Alternative((), empty), () )
import Control.Exception.Lifted
( ErrorCall(..),
throwIO )