title: Cannot install ghc-mod due to “unattainable version of base”
body: <p>I'm trying to install the ghc-mod library on Windows. Using <code>stack install ghc-mod</code> shows this lengthy error message:</p>
  
  <pre><code>Error: While constructing the build plan, the following exceptions were encountered:
  
  In the dependencies for ghc-mod-5.8.0.0:
      Cabal-2.4.1.0 from stack configuration does not match &gt;=1.18 &amp;&amp; &lt;1.25  (latest matching version is 1.24.2.0)
      base-4.12.0.0 from stack configuration does not match &gt;=4.6.0.1 &amp;&amp; &lt;4.10  (latest matching version is 4.9.1.0)
      cabal-helper must match &lt;0.8 &amp;&amp; &gt;=0.7.3.0, but the stack configuration has no specified version  (latest matching
                   version is 0.7.3.0)
      djinn-ghc must match &lt;0.1 &amp;&amp; &gt;=0.0.2.2, but the stack configuration has no specified version  (latest matching
                version is 0.0.2.3)
      extra-1.6.17 from stack configuration does not match &lt;1.6 &amp;&amp; &gt;=1.4  (latest matching version is 1.5.3)
      ghc-8.6.5 from stack configuration does not match &gt;=7.6 &amp;&amp; &lt;8.2
      ghc-syb-utils must match &lt;0.3 &amp;&amp; &gt;=0.2.3, but the stack configuration has no specified version  (latest matching
                    version is 0.2.3.3)
      haskell-src-exts-1.20.3 from stack configuration does not match &lt;1.20 &amp;&amp; &gt;=1.18  (latest matching version is 1.19.1)    hlint-2.1.11 from stack configuration does not match &lt;2.1 &amp;&amp; &gt;=2.0.8  (latest matching version is 2.0.15)
      monad-journal-0.8.1 from stack configuration does not match &lt;0.8 &amp;&amp; &gt;=0.4  (latest matching version is 0.7.2)
      optparse-applicative-0.14.3.0 from stack configuration does not match &gt;=0.13.0.0 &amp;&amp; &lt;0.14  (latest matching version
                                    is 0.13.2.0)
      temporary-1.3 from stack configuration does not match &lt;1.3 &amp;&amp; &gt;=1.2.0.3  (latest matching version is 1.2.1.1)
  needed since ghc-mod is a build target.
  
  Some different approaches to resolving this:
  
    * Build requires unattainable version of base. Since base is a part of GHC, you most likely need to use a different
      GHC version with the matching base.
  </code></pre>
  
  <p>Apparently, I need to change the version of ghc, but my version is higher than the one required, so updating doesn't help. Should I downgrade? How to do it without messing up the rest of my ghc ecosystem?</p>
  
  <p>Using cabal to install it gives similar results.</p>