nix-shell -A glpk-hs.env release.nix --run 'cabal configure && ghci -isrc'
nix-build release.nix
result/bin/glpk-hs-example
0: obj = -0.000000000e+00 inf = 0.000e+00 (3)
3: obj = 7.000000000e+02 inf = 0.000e+00 (0)
3: mip = not found yet <= +inf (1; 0)
3: >>>>> 7.000000000e+02 <= 7.000000000e+02 0.0% (1; 0)
3: mip = 7.000000000e+02 <= tree is empty 0.0% (0; 1)
(Success,Just (700.0,fromList [("x1",40.0),("x2",50.0),("x3",0.0)]))