Merge pull request #296272 from hsjobeki/lib/foldl-prime

lib.foldl': avoid unnecessary function call

lib/lists.nix

@@ -228,7 +228,15 @@ rec {
 
     `acc`
 
-    : The initial accumulator value
+    : The initial accumulator value.
+
+      The accumulator value is evaluated in any case before the first iteration starts.
+
+      To avoid evaluation even before the `list` argument is given an eta expansion can be used:
+
+      ```nix
+      list: lib.foldl' op acc list
+      ```
 
     `list`
 
@@ -254,13 +262,11 @@ rec {
   foldl' =
     op:
     acc:
-    list:
-
     # The builtin `foldl'` is a bit lazier than one might expect.
     # See https://github.com/NixOS/nix/pull/7158.
     # In particular, the initial accumulator value is not forced before the first iteration starts.
     builtins.seq acc
-      (builtins.foldl' op acc list);
+      (builtins.foldl' op acc);
 
   /**
     Map with index starting from 0