i have a file called model.hs with it’s content as
module Model (Foo) where
data Foo = Yellow | Red | Blue deriving Show
I have another file called sim.hs where I am trying to import Foo. The content of this file is
module Sim where
import Model.Foo
But this throws an error Could not find module Model.Foo. What am I doing wrong here?
Foo is a type that is defined in the module Model. In Haskell you can’t import types or functions directly like that. You can import the entire module: import Model or you can import specific functions/types from a module with the syntax: import Model (Foo). Here is the section of the Haskell2010 report that describes all possible ways of importing things. Maybe the most useful part is this table with examples:
| Import declaration | Names brought into scope |
| import A | x, y, A.x, A.y |
| import A() | (nothing) |
| import A(x) | x, A.x |
| import qualified A | A.x, A.y |
| import qualified A() | (nothing) |
| import qualified A(x) | A.x |
| import A hiding () | x, y, A.x, A.y |
| import A hiding (x) | y, A.y |
| import qualified A hiding () | A.x, A.y |
| import qualified A hiding (x) | A.y |
| import A as B | x, y, B.x, B.y |
| import A as B(x) | x, B.x |
| import qualified A as B | B.x, B.y |
In your case Model can be substituted for A or B, and Foo can be substituted for x or y.