diff --git a/tidepool/src/lib/packages.nix b/tidepool/src/lib/packages.nix
index 6114e6a..0759866 100644
--- a/tidepool/src/lib/packages.nix
+++ b/tidepool/src/lib/packages.nix
@@ -16,7 +16,7 @@ in
 
         build =
           build: host: target:
-          builtins.mapAttrs (name: dep: dep.packages.${build}.${host}.${target});
+          builtins.mapAttrs (name: dep: (lib.packages.resolve dep).packages.${build}.${host}.${target});
 
         collect =
           package:
@@ -28,8 +28,9 @@ in
               dependencies:
               let
                 getDeps =
-                  name: dependency:
+                  name: dep:
                   let
+                    dependency = lib.packages.resolve dep;
                     deps = {
                       build = {
                         build =
@@ -61,19 +62,21 @@ in
                 propagated = lib.attrs.mapToList getDeps dependencies;
               in
               lib.lists.flatten propagated;
+
+            withoutNulls = deps: builtins.filter (dep: dep != null) deps;
           in
           {
             build = {
-              build = builtins.attrValues package.deps.build.build ++ process package.deps.build.build;
-              host = builtins.attrValues package.deps.build.host ++ process package.deps.build.host;
-              target = builtins.attrValues package.deps.build.target ++ process package.deps.build.target;
+              build = withoutNulls (builtins.attrValues package.deps.build.build ++ process package.deps.build.build);
+              host = withoutNulls (builtins.attrValues package.deps.build.host ++ process package.deps.build.host);
+              target = withoutNulls (builtins.attrValues package.deps.build.target ++ process package.deps.build.target);
             };
             host = {
-              host = builtins.attrValues package.deps.host.host ++ process package.deps.host.host;
-              target = builtins.attrValues package.deps.host.target ++ process package.deps.host.target;
+              host = withoutNulls (builtins.attrValues package.deps.host.host ++ process package.deps.host.host);
+              target = withoutNulls (builtins.attrValues package.deps.host.target ++ process package.deps.host.target);
             };
             target = {
-              target = builtins.attrValues package.deps.target.target ++ process package.deps.target.target;
+              target = withoutNulls (builtins.attrValues package.deps.target.target ++ process package.deps.target.target);
             };
           };
       };
@@ -83,9 +86,9 @@ in
           package: collected: ctx:
           let
             process =
-              path:
+              path: deps:
               let
-                dependencies = lib.attrs.selectOrThrow path collected;
+                dependencies = lib.lists.flatten deps;
                 contexts = builtins.map (dependency: dependency.context or { }) dependencies;
                 result = lib.modules.run {
                   args = {
@@ -93,8 +96,9 @@ in
                   };
 
                   prefix = package.__module__.args.dynamic.meta.prefix ++ [
-                    "<context ${builtins.concatStringsSep path}>"
+                    "<context ${path}>"
                   ];
+
                   modules = (builtins.map (context: { config = context; }) contexts) ++ [
                     {
                       freeform = lib.types.any;
@@ -103,22 +107,12 @@ in
                         target = lib.options.create {
                           description = "The dependency target that is being generated.";
                           type = lib.types.enum [
-                            "build.build"
-                            "build.host"
-                            "build.target"
-                            "host.host"
-                            "host.target"
-                            "target.target"
+                            "build"
+                            "host"
+                            "target"
                           ];
                           writable = false;
-                          default.value = builtins.concatStringsSep "." path;
-                        };
-
-                        deps = lib.options.create {
-                          description = "The collected dependencies.";
-                          writable = false;
-                          default.value = collected;
-                          type = lib.types.dependencies;
+                          default.value = path;
                         };
                       };
 
@@ -128,38 +122,34 @@ in
                 };
               in
               result.config;
+
+            build = process "build" [ collected.build.build collected.build.host collected.build.target ];
+            host = process "host" [ collected.host.host collected.host.target ];
+            target = process "target" [ collected.target.target ];
           in
+          build // host //
           {
-            build = {
-              build = process [
-                "build"
-                "build"
-              ];
-              host = process [
-                "build"
-                "host"
-              ];
-              target = process [
-                "build"
-                "target"
-              ];
-            };
-            host = {
-              host = process [
-                "host"
-                "host"
-              ];
-              target = process [
-                "host"
-                "target"
-              ];
-            };
-            target = {
-              target = process [
-                "target"
-                "target"
-              ];
-            };
+            inherit build host target;
+
+            deps = collected;
+
+            __toString = value:
+              let
+                all = builtins.mapAttrs
+                  (host: targets:
+                    builtins.mapAttrs
+                      (target: deps:
+                        builtins.map (dep: dep.package) deps
+                      )
+                      targets
+                  )
+                  collected;
+              in
+              builtins.toJSON (
+                builtins.removeAttrs value [ "deps" "__toString" ] // {
+                  deps = all;
+                }
+              );
           };
       };
 
@@ -171,9 +161,9 @@ in
               path:
               let
                 dependencies = lib.attrs.selectOrThrow path collected;
-                hooks = builtins.map (
-                  dependency: if builtins.isFunction dependency.hooks then dependency.hooks ctx else dependency.hooks
-                ) dependencies;
+                hooks = builtins.map
+                  (dependency: if builtins.isFunction dependency.hooks then dependency.hooks ctx else dependency.hooks)
+                  dependencies;
               in
               hooks;
           in
@@ -270,9 +260,11 @@ in
         alias: build: host: target:
         let
           package = lib.packages.resolve alias;
-          matches = builtins.filter (
-            platform: platform.build == build && platform.host == host && platform.target == target
-          ) package.platforms;
+          matches = builtins.filter
+            (
+              platform: platform.build == build && platform.host == host && platform.target == target
+            )
+            package.platforms;
         in
         {
           compatible =
diff --git a/tidepool/src/lib/types.nix b/tidepool/src/lib/types.nix
index 051a934..6b327c0 100644
--- a/tidepool/src/lib/types.nix
+++ b/tidepool/src/lib/types.nix
@@ -152,9 +152,11 @@ in
             merge =
               location: definitions:
               let
-                modules = builtins.concatMap (
-                  definition: lib.lists.from.any (normalize definition.value)
-                ) definitions;
+                modules = builtins.concatMap
+                  (
+                    definition: lib.lists.from.any (normalize definition.value)
+                  )
+                  definitions;
 
                 result = lib.modules.run {
                   prefix = location;
@@ -173,10 +175,10 @@ in
           };
 
           submodule =
-            {
-              config,
-              meta,
-              name ? "builder",
+            { config
+            , meta
+            , name ? "builder"
+            ,
             }:
             {
               options = {
@@ -288,26 +290,32 @@ in
           transform =
             value:
             let
-              result = builtins.mapAttrs (
-                namespace: aliases:
-                builtins.mapAttrs (
-                  id: alias:
-                  alias
-                  // {
-                    versions = builtins.mapAttrs (version: package: {
-                      __modules__ = (lib.lists.from.any (normalize package)) ++ [
-                        {
-                          config = {
-                            id = lib.modules.overrides.default id;
-                            version = lib.modules.overrides.default version;
-                            namespace = lib.modules.overrides.default namespace;
-                          };
-                        }
-                      ];
-                    }) alias.versions;
-                  }
-                ) aliases
-              ) value;
+              result = builtins.mapAttrs
+                (
+                  namespace: aliases:
+                    builtins.mapAttrs
+                      (
+                        id: alias:
+                          alias
+                          // {
+                            versions = builtins.mapAttrs
+                              (version: package: {
+                                __modules__ = (lib.lists.from.any (normalize package)) ++ [
+                                  {
+                                    config = {
+                                      id = lib.modules.overrides.default id;
+                                      version = lib.modules.overrides.default version;
+                                      namespace = lib.modules.overrides.default namespace;
+                                    };
+                                  }
+                                ];
+                              })
+                              alias.versions;
+                          }
+                      )
+                      aliases
+                )
+                value;
             in
             result;
 
@@ -405,8 +413,8 @@ in
                 let
                   default = config.${global.config.preferences.packages.version};
                 in
-                default.extend
-                  or (builtins.throw "Package \"${name}\" does not have a ${global.config.preferences.packages.version} release.");
+                  default.extend
+                    or (builtins.throw "Package \"${name}\" does not have a ${global.config.preferences.packages.version} release.");
             };
 
             stable = lib.options.create {
@@ -488,9 +496,11 @@ in
             merge =
               location: definitions:
               let
-                modules = builtins.concatMap (
-                  definition: lib.lists.from.any (normalize definition.value)
-                ) definitions;
+                modules = builtins.concatMap
+                  (
+                    definition: lib.lists.from.any (normalize definition.value)
+                  )
+                  definitions;
 
                 result = lib.modules.run {
                   prefix = location;
@@ -557,9 +567,9 @@ in
             };
 
           submodule =
-            {
-              config,
-              meta,
+            { config
+            , meta
+            ,
             }:
             let
               build = config.platform.build;
@@ -577,10 +587,10 @@ in
 
                 __toString = lib.options.create {
                   description = "The derivation of the package as a string.";
-                  type = lib.types.string;
+                  type = lib.types.function lib.types.string;
                   internal = true;
                   writable = false;
-                  default.value = builtins.toString config.package;
+                  default.value = value: builtins.toString value.package;
                 };
 
                 extend = lib.options.create {
@@ -899,7 +909,7 @@ in
                 phases = lib.options.create {
                   description = "The phases for the package.";
                   type = lib.types.either (lib.types.dag.of lib.types.string) (
-                    lib.types.function lib.types.dag.of lib.types.string
+                    lib.types.function (lib.types.dag.of lib.types.string)
                   );
                   default.value = { };
                 };
diff --git a/tidepool/src/packages/aux/a.nix b/tidepool/src/packages/aux/a.nix
index 37fd58c..692adff 100644
--- a/tidepool/src/packages/aux/a.nix
+++ b/tidepool/src/packages/aux/a.nix
@@ -33,9 +33,15 @@ in
               inherit (packages.aux) b;
             };
 
-            phases = {
+            phases = ctx: {
               install = ''
-                echo "a with b: ${config.deps.host.host.b.platform.host.double}" > $out
+                echo "a with b: ${config.deps.host.host.b.platform.host}" > $out
+                echo >> $out
+                echo a=$out >> $out
+                echo b=$AUX_B >> $out
+                echo c=$AUX_C >> $out
+                echo >> $out
+                echo '${ctx}' >> $out
               '';
             };
           };
diff --git a/tidepool/src/packages/foundation/default.nix b/tidepool/src/packages/foundation/default.nix
index cecab3a..1c3eed6 100644
--- a/tidepool/src/packages/foundation/default.nix
+++ b/tidepool/src/packages/foundation/default.nix
@@ -1,3 +1,7 @@
+{ config }:
+let
+  inherit (config) lib;
+in
 {
   includes = [
     ./bash
@@ -25,4 +29,14 @@
     ./xz
     ./zlib
   ];
+
+  config = {
+    packages.context.options = {
+      "foundation:cflags" = lib.options.create {
+        description = "C compiler flags used by the foundation compiler toolchain.";
+        type = lib.types.list.of lib.types.string;
+        default.value = [ ];
+      };
+    };
+  };
 }