lib: ip: add 'nthInRange4'

And use it to refactor 'rangeIp4'

lib/ip.nix

@@ -86,15 +86,8 @@ rec {
   # Pretty print a parsed subnet into a human readable form
   prettySubnet4 = { baseIp, cidr, ... }: "${prettyIp4 baseIp}/${toString cidr}";
 
-  # Convert an IPv4 range into a list of all its constituent addresses
-  rangeIp4 =
-    { from, to }:
-    let
-      numAddresses =
-        builtins.foldl' (acc: rhs: acc * 256 + rhs)
-          0
-          (zipListsWith (lhs: rhs: lhs - rhs) to from);
-      addToBase = n:
+  # Get the nth address from an IPv4 range, without checking if it is in range
+  nthInRange4 = { from, to }: n:
     let
       carry = lhs: { carry, acc }:
         let
@@ -107,6 +100,15 @@ rec {
       carried = foldr carry { carry = n; acc = [ ]; } from;
     in
     carried.acc;
+
+  # Convert an IPv4 range into a list of all its constituent addresses
+  rangeIp4 =
+    { from, to } @ arg:
+    let
+      numAddresses =
+        builtins.foldl' (acc: rhs: acc * 256 + rhs)
+          0
+          (zipListsWith (lhs: rhs: lhs - rhs) to from);
     in
-    map addToBase (range 0 numAddresses);
+    map (nthInRange4 arg) (range 0 numAddresses);
 }