···

       
5
       
5
       
 
       


     

       
6
       
6
       
 
       
* [`dhall-lang.org` - Installing packages](https://docs.dhall-lang.org/tutorials/Language-Tour.html#installing-packages)

     

       
7
       
7
       
 
       


     

       
8
       
8
       
-
       
## Remote imports

     

       
8
       
8
       
+
       
## Remote imports {#ssec-dhall-remote-imports}

     

       
9
       
9
       
 
       


     

       
10
       
10
       
 
       
Nixpkgs bypasses Dhall's support for remote imports using Dhall's

     

       
11
       
11
       
 
       
semantic integrity checks.  Specifically, any Dhall import can be protected by

     
···

       
32
       
32
       
 
       
to fetch Dhall code ensures that Dhall packages built using Nix remain pure and

     

       
33
       
33
       
 
       
also behave well when built within a sandbox.

     

       
34
       
34
       
 
       


     

       
35
       
35
       
-
       
## Packaging a Dhall expression from scratch

     

       
35
       
35
       
+
       
## Packaging a Dhall expression from scratch {#ssec-dhall-packaging-expression}

     

       
36
       
36
       
 
       


     

       
37
       
37
       
 
       
We can illustrate how Nixpkgs integrates Dhall by beginning from the following

     

       
38
       
38
       
 
       
trivial Dhall expression with one dependency (the Prelude):

     
···

       
117
       
117
       
 
       
$ nix build --file ./example.nix dhallPackages.true

     

       
118
       
118
       
 
       
```

     

       
119
       
119
       
 
       


     

       
120
       
120
       
-
       
## Contents of a Dhall package

     

       
120
       
120
       
+
       
## Contents of a Dhall package {#ssec-dhall-package-contents}

     

       
121
       
121
       
 
       


     

       
122
       
122
       
 
       
The above package produces the following directory tree:

     

       
123
       
123
       
 
       


     
···

       
224
       
224
       
 
       
…

     

       
225
       
225
       
 
       
```

     

       
226
       
226
       
 
       


     

       
227
       
227
       
-
       
## Packaging functions

     

       
227
       
227
       
+
       
## Packaging functions {#ssec-dhall-packaging-functions}

     

       
228
       
228
       
 
       


     

       
229
       
229
       
 
       
We already saw an example of using `buildDhallPackage` to create a Dhall

     

       
230
       
230
       
 
       
package from a single file, but most Dhall packages consist of more than one

     
···

       
297
       
297
       
 
       
Additionally, `buildDhallGitHubPackage` accepts the same arguments as

     

       
298
       
298
       
 
       
`fetchFromGitHub`, such as `sha256` or `fetchSubmodules`.

     

       
299
       
299
       
 
       


     

       
300
       
300
       
-
       
## `dhall-to-nixpkgs`

     

       
300
       
300
       
+
       
## `dhall-to-nixpkgs` {#ssec-dhall-dhall-to-nixpkgs}

     

       
301
       
301
       
 
       


     

       
302
       
302
       
 
       
You can use the `dhall-to-nixpkgs` command-line utility to automate

     

       
303
       
303
       
 
       
packaging Dhall code.  For example:

     
···

       
342
       
342
       
 
       
    }

     

       
343
       
343
       
 
       
```

     

       
344
       
344
       
 
       


     

       
345
       
345
       
-
       
## Overriding dependency versions

     

       
345
       
345
       
+
       
## Overriding dependency versions {#ssec-dhall-overriding-dependency-versions}

     

       
346
       
346
       
 
       


     

       
347
       
347
       
 
       
Suppose that we change our `true.dhall` example expression to depend on an older

     

       
348
       
348
       
 
       
version of the Prelude (19.0.0):

     
···

       
415
       
415
       
 
       
  };

     

       
416
       
416
       
 
       
```

     

       
417
       
417
       
 
       


     

       
418
       
418
       
-
       
## Overrides

     

       
418
       
418
       
+
       
## Overrides {#ssec-dhall-overrides}

     

       
419
       
419
       
 
       


     

       
420
       
420
       
 
       
You can override any of the arguments to `buildDhallGitHubPackage` or

     

       
421
       
421
       
 
       
`buildDhallDirectoryPackage` using the `overridePackage` attribute of a package.