Add dhall support

snack-lib/files.nix

@@ -50,6 +50,12 @@ rec {
   doesFileExist = base: filename:
     lib.lists.elem filename (listFilesInDir base);
 
+  fileExtension = fp:
+    let
+      exts = lib.splitString "." (builtins.baseNameOf fp);
+    in if lib.length exts == 0 then null else lib.last exts;
+
+
   listFilesInDir = dir:
   let
     go = dir: dirName:

snack-lib/hpack.nix

@@ -1,6 +1,7 @@
-{ lib, glibcLocales, callPackage, writeText, runCommand, haskellPackages }:
+{ lib, dhall-json, glibcLocales, callPackage, writeText, runCommand, haskellPackages }:
 
 with (callPackage ./lib.nix {});
+with (callPackage ./files.nix {});
 with (callPackage ./modules.nix {});
 
 let
@@ -19,14 +20,38 @@ let
         "${y2j} ${writeText "y2j" text}  > $out"
         );
       in builtins.fromJSON json;
+
+    fromDhall = text:
+      let json =
+
+        builtins.readFile (runCommand "d2j"
+          { buildInputs = [ dhall-json ]; }
+        # hack: dhall-to-json gets a path and then imports the contents
+        "dhall-to-json <<< ${writeText "d2j" text}  > $out"
+        );
+      in builtins.fromJSON json;
 in
 {
   # Returns an attribute set with two fields:
   #  - library: a package spec
   #  - executable: an attr set of executable name to package spec
   pkgDescrsFromHPack = packageYaml:
     let
-        package = fromYAML (builtins.readFile packageYaml);
+        package =
+          let
+            ext = fileExtension packageYaml;
+            fromFile =
+            if ext == null
+              then abort "File ${packageYaml} has no extension!"
+              else if ext == "yaml"
+              then fromYAML
+              else if ext == "yml"
+              then fromYAML
+              else if ext == "dhall"
+              then fromDhall
+              else
+                abort "File ${packageYaml} has an unknown extension (${ext})!";
+          in fromFile (builtins.readFile packageYaml);
 
         # Snack drops the version bounds because here it has no meaning
         dropVersionBounds =

tests/readme/package.dhall

@@ -0,0 +1,16 @@
+{ name = "snack-readme"
+
+, dependencies =
+    [ "lens", "wreq" ]
+
+, library =
+    { source-dirs = "./src" }
+
+, executable =
+    { main = "Main.hs"
+    , source-dirs = "./app"
+    , dependencies = [ "snack-readme" ]
+    }
+
+, default-extensions = [ "OverloadedStrings" ]
+}

tests/readme/test

@@ -11,3 +11,4 @@ test() {
 SNACK="snack" test
 SNACK="snack -s ./snack.nix" test
 SNACK="snack --package-yaml ./package.yaml" test
+SNACK="snack --package-yaml ./package.dhall" test