lib.lists: add `replicate`

`replicate` returns n copies of an element as a list.

Co-Authored-By: Silvan Mosberger <contact@infinisil.com>

3 files changed, 18 insertions, 1 deletions

diff --git a/lib/default.nix b/lib/default.nix
index 68e5b8dea1e..9fa3f4175a2 100644
--- a/lib/default.nix
+++ b/lib/default.nix
@@ -87,7 +87,7 @@ let
       updateManyAttrsByPath;
     inherit (self.lists) singleton forEach foldr fold foldl foldl' imap0 imap1
       concatMap flatten remove findSingle findFirst any all count
-      optional optionals toList range partition zipListsWith zipLists
+      optional optionals toList range replicate partition zipListsWith zipLists
       reverseList listDfs toposort sort naturalSort compareLists take
       drop sublist last init crossLists unique intersectLists
       subtractLists mutuallyExclusive groupBy groupBy';
diff --git a/lib/lists.nix b/lib/lists.nix
index 602b13cf69c..32b3f06b195 100644
--- a/lib/lists.nix
+++ b/lib/lists.nix
@@ -303,6 +303,18 @@ rec {
     else
       genList (n: first + n) (last - first + 1);
 
+  /* Return a list with `n` copies of an element.
+
+    Type: replicate :: int -> a -> [a]
+
+    Example:
+      replicate 3 "a"
+      => [ "a" "a" "a" ]
+      replicate 2 true
+      => [ true true ]
+  */
+  replicate = n: elem: genList (_: elem) n;
+
   /* Splits the elements of a list in two lists, `right` and
      `wrong`, depending on the evaluation of a predicate.
 
diff --git a/lib/tests/misc.nix b/lib/tests/misc.nix
index c719fcf5d4f..7e52a2e8f0a 100644
--- a/lib/tests/misc.nix
+++ b/lib/tests/misc.nix
@@ -459,6 +459,11 @@ runTests {
     expected = [2 30 40 42];
   };
 
+  testReplicate = {
+    expr = replicate 3 "a";
+    expected = ["a" "a" "a"];
+  };
+
   testToIntShouldConvertStringToInt = {
     expr = toInt "27";
     expected = 27;