bool.guard

2 files changed, 47 insertions, 0 deletions

diff --git a/src/gleam/bool.gleam b/src/gleam/bool.gleam
index e67fe66..c64ee97 100644
--- a/src/gleam/bool.gleam
+++ b/src/gleam/bool.gleam
@@ -323,3 +323,36 @@ pub fn to_string(bool: Bool) -> String {
     True -> "True"
   }
 }
+
+/// Run a callback function if the given bool is `True`, otherwise return a
+/// default value.
+///
+/// This function is suitable for `use` expressions.
+///
+/// ## Examples
+///
+/// ```gleam
+/// > let name = "Kamaka"
+/// > use <- guard(name != "", or: "friend")
+/// > "Hello, " <> name
+/// "Hello, Kamaka"
+/// ```
+///
+/// ```gleam
+/// > let name = ""
+/// > use <- guard(name != "", or: "friend")
+/// > "Hello, " <> name
+/// "Hello, friend"
+/// ```
+///
+///
+pub fn guard(
+  requirement: Bool,
+  or alternative: t,
+  then consequence: fn() -> t,
+) -> t {
+  case requirement {
+    True -> consequence()
+    False -> alternative
+  }
+}
diff --git a/test/gleam/bool_test.gleam b/test/gleam/bool_test.gleam
index a362186..ab9e2de 100644
--- a/test/gleam/bool_test.gleam
+++ b/test/gleam/bool_test.gleam
@@ -155,3 +155,17 @@ pub fn to_string_test() {
   bool.to_string(False)
   |> should.equal("False")
 }
+
+pub fn guard_test() {
+  assert 1 = {
+    let x = 1
+    use <- bool.guard(True, or: 2)
+    x
+  }
+
+  assert 2 = {
+    let x = 1
+    use <- bool.guard(False, or: 2)
+    x
+  }
+}