Use foldl' instead of fold in some places

lib/lists.nix

@@ -38,6 +38,10 @@ rec {
     in foldl' (length list - 1);
 
 
+  # Strict version of foldl.
+  foldl' = builtins.foldl' or foldl;
+
+
   # map with index: `imap (i: v: "${v}-${toString i}") ["a" "b"] ==
   # ["a-1" "b-2"]'
   imap = f: list:
@@ -59,7 +63,7 @@ rec {
   # == [1 2 3 4 5]' and `flatten 1 == [1]'.
   flatten = x:
     if isList x
-    then fold (x: y: (flatten x) ++ y) [] x
+    then foldl' (x: y: x ++ (flatten y)) [] x
     else [x];
 
 
@@ -96,7 +100,7 @@ rec {
 
   # Count how many times function `pred' returns true for the elements
   # of `list'.
-  count = pred: fold (x: c: if pred x then c + 1 else c) 0;
+  count = pred: foldl' (c: x: if pred x then c + 1 else c) 0;
 
 
   # Return a singleton list or an empty list, depending on a boolean

lib/modules.nix

@@ -76,8 +76,8 @@ rec {
           else yieldConfig (prefix ++ [n]) v) set) ["_definedNames"];
         in
         if options._module.check.value && set ? _definedNames then
-          fold (m: res:
-            fold (name: res:
+          foldl' (res: m:
+            foldl' (res: name:
               if set ? ${name} then res else throw "The option `${showOption (prefix ++ [name])}' defined in `${m.file}' does not exist.")
               res m.names)
             res set._definedNames
@@ -225,7 +225,7 @@ rec {
      'opts' is a list of modules.  Each module has an options attribute which
      correspond to the definition of 'loc' in 'opt.file'. */
   mergeOptionDecls = loc: opts:
-    fold (opt: res:
+    foldl' (res: opt:
       if opt.options ? default && res ? default ||
          opt.options ? example && res ? example ||
          opt.options ? description && res ? description ||
@@ -251,7 +251,7 @@ rec {
             else if opt.options ? options then map (coerceOption opt.file) options' ++ res.options
             else res.options;
         in opt.options // res //
-          { declarations = [opt.file] ++ res.declarations;
+          { declarations = res.declarations ++ [opt.file];
             options = submodules;
           }
     ) { inherit loc; declarations = []; options = []; } opts;
@@ -302,8 +302,8 @@ rec {
         in
           processOrder (processOverride (processIfAndMerge defs));
 
-        # Type-check the remaining definitions, and merge them
-        mergedValue = fold (def: res:
+        # Type-check the remaining definitions, and merge them.
+        mergedValue = foldl' (res: def:
           if type.check def.value then res
           else throw "The option value `${showOption loc}' in `${def.file}' is not a ${type.name}.")
           (type.merge loc defsFinal) defsFinal;
@@ -384,7 +384,7 @@ rec {
       defaultPrio = 100;
       getPrio = def: if def.value._type or "" == "override" then def.value.priority else defaultPrio;
       min = x: y: if x < y then x else y;
-      highestPrio = fold (def: prio: min (getPrio def) prio) 9999 defs;
+      highestPrio = foldl' (prio: def: min (getPrio def) prio) 9999 defs;
       strip = def: if def.value._type or "" == "override" then def // { value = def.value.content; } else def;
     in concatMap (def: if getPrio def == highestPrio then [(strip def)] else []) defs;
 

lib/options.nix

@@ -53,8 +53,8 @@ rec {
     if length list == 1 then head list
     else if all isFunction list then x: mergeDefaultOption loc (map (f: f x) list)
     else if all isList list then concatLists list
-    else if all isAttrs list then fold lib.mergeAttrs {} list
-    else if all isBool list then fold lib.or false list
+    else if all isAttrs list then foldl' lib.mergeAttrs {} list
+    else if all isBool list then foldl' lib.or false list
     else if all isString list then lib.concatStrings list
     else if all isInt list && all (x: x == head list) list then head list
     else throw "Cannot merge definitions of `${showOption loc}' given in ${showFiles (getFiles defs)}.";
@@ -68,7 +68,7 @@ rec {
   /* "Merge" option definitions by checking that they all have the same value. */
   mergeEqualOption = loc: defs:
     if defs == [] then abort "This case should never happen."
-    else fold (def: val:
+    else foldl' (val: def:
       if def.value != val then
         throw "The option `${showOption loc}' has conflicting definitions, in ${showFiles (getFiles defs)}."
       else

lib/strings.nix

@@ -12,7 +12,7 @@ rec {
 
 
   # Concatenate a list of strings.
-  concatStrings = lib.fold (x: y: x + y) "";
+  concatStrings = lib.foldl' (x: y: x + y) "";
 
 
   # Map a function over a list and concatenate the resulting strings.

lib/types.nix

@@ -88,7 +88,7 @@ rec {
     attrs = mkOptionType {
       name = "attribute set";
       check = isAttrs;
-      merge = loc: fold (def: mergeAttrs def.value) {};
+      merge = loc: foldl' (res: def: mergeAttrs res def.value) {};
     };
 
     # derivation is a reserved keyword.