Allow 'environment' to be attrset

example/flake.nix

@@ -19,11 +19,11 @@
         # This adds a `self.packages.default`
         process-compose."default" = {
           settings = {
-            environment = [
-              "DATAFILE=data.sqlite"
-            ];
-            processes = {
+            environment = {
+              DATAFILE = "data.sqlite";
+            };
 
+            processes = {
               # Print a pony every 2 seconds, because why not.
               ponysay.command = ''
                 while true; do

nix/process-compose/settings/environment.nix

@@ -1,6 +1,20 @@
 { lib, ... }:
+let
+  inherit (lib) types;
+  inherit (types) nullOr either listOf str attrsOf;
+in
 lib.mkOption {
-  type = lib.types.nullOr (lib.types.listOf lib.types.str);
+  type = 
+    nullOr 
+      (either (listOf str) (attrsOf str));
   default = null;
-  example = [ "ABC=2221" "PRINT_ERR=111" ];
+  example = { ABC="2221"; PRINT_ERR="111"; };
+  description = ''
+    Attrset of environment variables.
+
+    List of strings is also allowed.
+  '';
+  apply = attrs:
+    if ! builtins.isAttrs attrs then attrs else 
+    lib.mapAttrsToList (name: value: "${name}=${value}") attrs;
 }