From 3825c8568cbd6b5c2c0686554203680c4415f9b6 Mon Sep 17 00:00:00 2001
From: Gabriel Arazas <foodogsquared@foodogsquared.one>
Date: Tue, 4 Jun 2024 19:45:29 +0800
Subject: [PATCH] bahaghari/lib: add `trivial.optionalNull`

---
 subprojects/bahaghari/lib/trivial.nix          | 18 ++++++++++++++++++
 .../bahaghari/tests/lib/trivial/default.nix    | 10 ++++++++++
 2 files changed, 28 insertions(+)

diff --git a/subprojects/bahaghari/lib/trivial.nix b/subprojects/bahaghari/lib/trivial.nix
index f70f3eee..bbaa1818 100644
--- a/subprojects/bahaghari/lib/trivial.nix
+++ b/subprojects/bahaghari/lib/trivial.nix
@@ -195,4 +195,22 @@ rec {
   */
   scale = { inMin, inMax, outMin, outMax }: v:
     ((v - inMin) * (outMax - outMin)) / ((inMax - inMin) + outMin);
+
+  /* Returns a null value if the condition fails. Otherwise, returns the given
+     value `as`.
+
+     Type: optionalNull :: Bool -> Any -> Any
+
+     Example:
+      optionalNull true "HELLO"
+      => "HELLO"
+
+      optionalNull (null != null) "HELLO"
+      => null
+  */
+  optionalNull = cond: as:
+    if cond then
+      as
+    else
+      null;
 }
diff --git a/subprojects/bahaghari/tests/lib/trivial/default.nix b/subprojects/bahaghari/tests/lib/trivial/default.nix
index fd318e1d..278a8ab5 100644
--- a/subprojects/bahaghari/tests/lib/trivial/default.nix
+++ b/subprojects/bahaghari/tests/lib/trivial/default.nix
@@ -260,4 +260,14 @@ lib.runTests {
     expr = self.trivial.isNumber true;
     expected = false;
   };
+
+  testOptionalNull = {
+    expr = self.trivial.optionalNull true "HELLO";
+    expected = "HELLO";
+  };
+
+  testOptionalNull2 = {
+    expr = self.trivial.optionalNull false "HELLO";
+    expected = null;
+  };
 }