[nix-shell:~/development/freq]$ cabal new-build
Build profile: -w ghc-8.4.1 -O1
In order, the following will be built (use -v for more details):
 - freq-0.1.0.0 (lib) (file src/Freq/Internal.hs changed)
 - freq-0.1.0.0 (exe:freq-train) (configuration changed)
Preprocessing library for freq-0.1.0.0..
Building library for freq-0.1.0.0..
[1 of 2] Compiling Freq.Internal    ( src/Freq/Internal.hs, /home/dcartwright/development/freq/dist-newstyle/build/x86_64-linux/ghc-8.4.1/freq-0.1.0.0/build/Freq/Internal.o )
[2 of 2] Compiling Freq             ( src/Freq.hs, /home/dcartwright/development/freq/dist-newstyle/build/x86_64-linux/ghc-8.4.1/freq-0.1.0.0/build/Freq.o ) [Freq.Internal changed]
Configuring executable 'freq-train' for freq-0.1.0.0..
Preprocessing executable 'freq-train' for freq-0.1.0.0..
Building executable 'freq-train' for freq-0.1.0.0..
[1 of 1] Compiling Main             ( app/Main.hs, /home/dcartwright/development/freq/dist-newstyle/build/x86_64-linux/ghc-8.4.1/freq-0.1.0.0/x/freq-train/build/freq-train/freq-train-tmp/Main.o ) [Freq changed]
Linking /home/dcartwright/development/freq/dist-newstyle/build/x86_64-linux/ghc-8.4.1/freq-0.1.0.0/x/freq-train/build/freq-train/freq-train ...

[nix-shell:~/development/freq]$ cabal new-haddock
Up to date

[nix-shell:~/development/freq]$ rm -rf dist*

[nix-shell:~/development/freq]$ cabal new-haddock
Resolving dependencies...
Build profile: -w ghc-8.4.1 -O1
In order, the following will be built (use -v for more details):
 - freq-0.1.0.0 (lib) (first run)
Configuring library for freq-0.1.0.0..
Preprocessing library for freq-0.1.0.0..
Running Haddock on library for freq-0.1.0.0..
Haddock coverage:

src/Freq/Internal.hs:208:3: error:
    parse error on input ‘{-# UNPACK’
    |
208 |   {-# UNPACK #-} !ByteArray -- ^ Square two-dimensional array of Double, maps first char and second char to probability
    |   ^^^^^^^^^^
cabal: Failed to build documentation for freq-0.1.0.0.