Data.Matrixがないって言われる…
なぜ？

$ ghc connect4_4.hs

connect4_4.hs:3:8:
Could not find module ‘Data.Matrix’
Perhaps you meant
Data.Ratio (from base)
Data.Ratio (needs flag -package haskell2010-1.1.2.0)
Use -v to see a list of the files searched for.

$ ghc --version
The Glorious Glasgow Haskell Compilation System, version 7.8.3