Problem

I am reading Learn you a Haskell for great Good and I faced the problem of "attempting to use module ... which is not loaded" when I am at the end of chapter module, finally I got the solution on it

Steps of Solution

1. Load the source code
2. Set the module to Prelude
3. Import the modules

Load the source code

Compile the source code into the GHCI

*Geometry.Cuboid> :l Geometry/Cube.hs Geometry/Sphere.hs
[1 of 3] Compiling Geometry.Cuboid  ( Geometry/Cuboid.hs, interpreted )
[2 of 3] Compiling Geometry.Cube    ( Geometry/Cube.hs, interpreted )
[3 of 3] Compiling Geometry.Sphere  ( Geometry/Sphere.hs, interpreted )
Ok, modules loaded: Geometry.Sphere, Geometry.Cuboid, Geometry.Cube.

Set the module to Prelude

Change back the current module in the GHCI to Prelude, by default the last module loaded becomes the current module.

*Geometry.Cube> :module Prelude

Import the modules

Import the modules we just loaded in the GHCI, and you can see the qualified name of the module will be append into the namespace.

Prelude> import qualified Geometry.Sphere as Sphere 
Prelude Sphere> import qualified Geometry.Cuboid as Cuboid 
Prelude Sphere Cuboid> import qualified Geometry.Cube as Cube 
Prelude Sphere Cuboid Cube>