Add primop genList

This can be used to implement functions like ‘imap’ (or for that
matter, ‘map’) without the quadratic complexity incurred by calling
‘++’ repeatedly.

1 files changed, 3 insertions, 3 deletions

diff --git a/tests/lang/lib.nix b/tests/lang/lib.nix
index 262cdd7e8..028a53831 100644
--- a/tests/lang/lib.nix
+++ b/tests/lang/lib.nix
@@ -54,8 +54,8 @@ rec {
   const = x: y: x;
 
   range = first: last:
-    if builtins.lessThan last first
-    then []
-    else [first] ++ range (builtins.add first 1) last;
+    if first > last
+      then []
+      else genList (n: first + n) (last - first + 1);
 
 }