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Frequently Asked Questions

  1. How do I declare a new Haskell dependency?
  2. How do I add or override Haskell dependencies in the package set?
  3. How do I extend my Obelisk application with more local packages?
  4. How do I use ob run over HTTPS?
  5. How do I fix invalid entitlements?
  6. ob thunk update or ob deploy update fails
  7. How do I fix Ambiguous module name errors?
  8. How do I fix no C compiler provided for this platform errors?

How do I declare a new Haskell dependency?

Every component of your Obelisk application is a standard cabal package. That means declaring new Haskell dependencies simply involves updating the build-depends field in the appropriate cabal file (backend.cabal for example). By default, Obelisk will use its curated package set to choose which version of each package you get. It's possible that the package you need is not already in the curated set or the curated version isn't the one you want. See How do I add or override Haskell dependencies in the package set? for a solution to this.

How do I add or override Haskell dependencies in the package set?

To add a Haskell package that doesn't exist in Obelisk's package set or to override the version of a package, use the overrides attribute in your project's default.nix. For example, to use a specific version of the aeson package fetched from GitHub and a specific version of the waargonaut package fetched from Hackage, your default.nix will look like:

# ...
project ./. ({ pkgs, ... }: {
# ...
  overrides = self: super: let
    aesonSrc = pkgs.fetchFromGitHub {
      owner = "obsidiansystems";
      repo = "aeson-gadt-th";
      rev = "ed573c2cccf54d72aa6279026752a3fecf9c1383";
      sha256 = "08q6rnz7w9pn76jkrafig6f50yd0f77z48rk2z5iyyl2jbhcbhx3";
    };
  in
  {
    aeson = self.callCabal2nix "aeson" aesonSrc {};
    waargonaut = self.callHackageDirect {
      pkg = "waargonaut";
      ver = "0.8.0.1";
      sha256 = "1zv28np3k3hg378vqm89v802xr0g8cwk7gy3mr77xrzy5jbgpa39";
    } {};
  };
# ...

For further information see the Haskell section of nixpkgs "Contributors Guide".

How do I extend my Obelisk application with more local packages?

If the standard packages (frontend, backend, and common) are not enough, you may add more local packages by defining them with the packages attribute in your default.nix. The sources of these packages will be automatically loaded by ob run/ob repl/etc.

# ...
project ./. ({ pkgs, ... }: {
# ...
  packages = {
    another = ./dep/another;
  };
# ...

How do I use ob run over HTTPS?

To run your app locally over HTTPS, update the protocol in config/common/route to https, and then use ob run as normal.

Obelisk generates a self-signed certificate for running HTTPS so the browser will issue a warning about using an invalid certificate. On Chrome, you can go to chrome://flags/#allow-insecure-localhost to enable invalid certificates for localhost.

How do I fix invalid entitlements?

You probably did not set ios.bundleIdentifier correctly in default.nix. When this happens you'll see an error something like this:

2018-11-25 09:34:22.438 ios-deploy[58106:8521046] [ !! ] Error 0xe8008016: The executable was signed with invalid entitlements. AMDeviceSecureInstallApplication(0, device, url, options, install_callback, 0)

Fixing the value of ios.bundleIdentifier should fix the error.

ob thunk update or ob deploy update fails

Whenever an ob command fails, try re-running it with -v.

If you're using a private repo, and you get a failure in nix-prefetch-url, you may need to unpack and repack the thunk. Here's some example output that shows this issue:

Starting Obelisk </nix/store/j8wls8a89xr6s1a47lg6g83gnbdrfd0l-obelisk-command-0.1/bin/.ob-wrapped> args=["deploy","update","-v"] logging-level=Debug
Creating process: 'nix-build' './.obelisk/impl' '-A' 'command' '--no-out-link'
✔ Built  on ./.obelisk/impl [command]
Handing off to /nix/store/j8wls8a89xr6s1a47lg6g83gnbdrfd0l-obelisk-command-0.1/bin/ob
Starting Obelisk </nix/store/j8wls8a89xr6s1a47lg6g83gnbdrfd0l-obelisk-command-0.1/bin/.ob-wrapped> args=["--no-handoff","deploy","update","-v"] logging-level=Debug
Creating process: 'git' 'ls-remote' '--exit-code' '--symref' 'https://github.com/obsidiansystems/some-private-repo.git' 'refs/heads/master'
git ls-remote maps: (fromList [],fromList [(GitRef_Branch "master","8546dfc8be9653f20bb26214e0991dbb957cb290")])
Latest commit in branch master from remote repo https://github.com/obsidiansystems/some-private-repo.git is 8546dfc8be9653f20bb26214e0991dbb957cb290
Creating process: 'nix-prefetch-url' '--unpack' '--type' 'sha256' 'https://github.com/obsidiansystems/some-private-repo/archive/8546dfc8be9653f20bb26214e0991dbb957cb290.tar.gz'
error: unable to download 'https://github.com/obsidiansystems/some-private-repo/archive/8546dfc8be9653f20bb26214e0991dbb957cb290.tar.gz': HTTP error 404
Process exited with code 1; 'nix-prefetch-url' '--unpack' '--type' 'sha256' 'https://github.com/obsidiansystems/some-private-repo/archive/8546dfc8be9653f20bb26214e0991dbb957cb290.tar.gz'
nix-prefetch-url: Failed to determine sha256 hash of URL https://github.com/obsidiansystems/some-private-repo/archive/8546dfc8be9653f20bb26214e0991dbb957cb290.tar.gz
✖ Updating thunk ./src to latest

And here's how you can fix it:

ob thunk unpack $SOME_THUNK
ob thunk pack $SOME_THUNK

Substitute the directory of your thunk for $SOME_THUNK. In the case of ob deploy update, $SOME_THUNK will be src in the deployment directory.

(Based on issue #351).

How do I fix Ambiguous module name errors?

Since obelisk places the common/backend/frontend modules packages into the same ghci, and ghci doesn't "sandbox" them, it is possible to have conflicting module errors inside ob repl/watch/run that do not appear when doing a cabal build.

You can disambiguate this via PackageImports. For instance, if you see

error:
    Ambiguous module name ‘Crypto.Hash’:
      it was found in multiple packages:
      cryptohash-0.11.9 cryptonite-0.25

then specify the package you want in the import, e.g: import "cryptonite" Crypto.Hash

How do I fix no C compiler provided for this platform errors?

This can show up when when doing nix-build (ie for deployment).

This is probably because you have a package that needs a C compiler (like snap-core) in your common or frontend modules which need to be built for ghcjs which does not in fact have a C compiler. You'll need to remove those packages from your cabal files and rework your app to not need them in the frontend.