···

       
159
       
159
       
 
       
exactly one version. Those versions need to satisfy all the version constraints

     

       
160
       
160
       
 
       
given in the `.cabal` file of your package and all its dependencies.

     

       
161
       
161
       
 
       


     

       
162
       
162
       
-
       
The Haskell builder in nixpkgs, (described in more detail in

     

       
163
       
163
       
-
       
[#haskell-mkderivation]), does no such thing. It will simply take as input

     

       
164
       
164
       
-
       
packages with names off the desired dependencies and just check whether they

     

       
165
       
165
       
-
       
fulfill the version bounds and (by default, see `jailbreak`) fail if they

     

       
166
       
166
       
-
       
don’t.

     

       
162
       
162
       
+
       
The [Haskell builder in nixpkgs](#haskell-mkderivation) does no such thing.

     

       
163
       
163
       
+
       
It will simply take as input packages with names off the desired dependencies

     

       
164
       
164
       
+
       
and just check whether they fulfill the version bounds and (by default, see

     

       
165
       
165
       
+
       
`jailbreak`) fail if they don’t.

     

       
167
       
166
       
 
       


     

       
168
       
168
       
-
       
The package resolution is done by the `haskellPackages.callPackage` function,

     

       
167
       
167
       
+
       
The package resolution is done by the `haskellPackages.callPackage` function

     

       
169
       
168
       
 
       
which will, e.g., use `haskellPackages.aeson` for a package input of name

     

       
170
       
169
       
 
       
`aeson`.

     

       
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170
       
 
       
While this is the default behavior, it is possible to override the dependencies