Add contains to Listing

pkl-core/src/main/java/org/pkl/core/stdlib/base/ListingNodes.java

@@ -186,6 +186,23 @@ protected VmListing eval(VmListing self, VmFunction selector) {
     }
   }
 
+  public abstract static class contains extends ExternalMethod1Node {
+    @Specialization
+    protected boolean eval(VmListing self, Object element) {
+      var result = new MutableBoolean(false);
+      self.forceAndIterateMemberValues(
+          (key, member, value) -> {
+            if (element.equals(value)) {
+              result.set(true);
+              return false;
+            }
+            return true;
+          });
+      LoopNode.reportLoopCount(this, self.getLength());
+      return result.get();
+    }
+  }
+
   public abstract static class fold extends ExternalMethod2Node {
     @Child private ApplyVmFunction2Node applyLambdaNode = ApplyVmFunction2NodeGen.create();
 

pkl-core/src/test/files/LanguageSnippetTests/input/api/listing.pkl

@@ -23,6 +23,10 @@ local duplicate: Listing<Person> = (base) {
   new { name = "Elf Owl" }
 }
 
+local altered: Listing<Person> = (base) {
+  [0] { name = "Wood Pigeon" }
+}
+
 facts {
   ["isEmpty"] {
     empty.isEmpty
@@ -112,6 +116,14 @@ facts {
     base.singleOrNull == null
     new Listing { 42 }.singleOrNull == 42
   }
+
+  ["contains"] {
+    !empty.contains(0)
+    base.contains(base[1])
+    derived.contains(base[1])
+    derived.contains(derived[3])
+    !altered.contains(base[0])
+  }
 }
 
 examples {

pkl-core/src/test/files/LanguageSnippetTests/output/api/listing.pcf

@@ -75,6 +75,13 @@ facts {
     true
     true
   }
+  ["contains"] {
+    true
+    true
+    true
+    true
+    true
+  }
 }
 examples {
   ["length"] {

stdlib/base.pkl

@@ -1916,6 +1916,17 @@ class Listing<out Element> extends Object {
   @AlsoKnownAs { names { "uniqueBy" } }
   external function distinctBy(selector: (Element) -> Any): Listing<Element>
 
+  /// Tests if [element] is contained in this listing.
+  ///
+  /// Facts:
+  /// ```
+  /// new Listing { 1 ; 2 ; 3 }.contains(1)
+  /// new Listing { 1 ; 2 ; 3 }.contains(2)
+  /// new Listing { 1 ; 2 ; 3 }.contains(3)
+  /// !new Listing { 1 ; 2 ; 3 }.contains(4)
+  /// ```
+  external function contains(element: Element): Boolean
+
   /// Folds this listing in iteration order using [operator], starting with [initial].
   external function fold<Result>(initial: Result, operator: (Result, Element) -> Result): Result