Install libghc-fgl-doc by entering the following commands in the terminal:
sudo apt update sudo apt install libghc-fgl-doc
Description:
Haskell graph library for GHC; documentation
This is Martin Erwig's Functional Graph Library. . This package provides the documentation for a library for the Haskell programming language. See http://www.haskell.org/ for more information on Haskell.
Homepage: http://hackage.haskell.org/package/fgl
Version: 5.5.4.0-1
Section: universe/doc