Add tagged unions example from chatgpt.

Author: cristianoc

jscomp/test/variantsMatching.js

@@ -345,6 +345,23 @@ var MyNullableExtended = {
   expectSeven: expectSeven$1
 };
 
+function area(shape) {
+  switch (shape.TAG) {
+    case "Circle" :
+        return Math.PI * Math.pow(shape._0.radius, 2);
+    case "Square" :
+        return Math.pow(shape._0.sideLength, 2);
+    case "Rectangle" :
+        var match = shape._0;
+        return match.width * match.height;
+    
+  }
+}
+
+var TaggedUnions = {
+  area: area
+};
+
 exports.toEnum = toEnum;
 exports.toString = toString;
 exports.bar = bar;
@@ -360,4 +377,5 @@ exports.MyUndefined = MyUndefined;
 exports.MyNull = MyNull;
 exports.MyNullable = MyNullable;
 exports.MyNullableExtended = MyNullableExtended;
+exports.TaggedUnions = TaggedUnions;
 /* expectSeven Not a pure module */

jscomp/test/variantsMatching.res

@@ -204,3 +204,65 @@ module MyNullableExtended = {
   let expectSeven = plus(Present({x: 4., y: 3.}), Present({x: 3., y: 4.}))
   Js.log2("expect {x:7, y:7}:", expectSeven)
 }
+module TaggedUnions = {
+  /*
+  type Circle = {
+    kind: 1; // Number literal
+    radius: number;
+  };
+
+  type Square = {
+    kind: "square"; // String literal
+    sideLength: number;
+  };
+
+  type Rectangle = {
+    kind: "rectangle"; // String literal
+    width: number;
+    height: number;
+  };
+
+  type Shape = Circle | Square | Rectangle;
+
+  function area(shape: Shape): number {
+    switch (shape.kind) {
+      case 1: // Circle
+        return Math.PI * shape.radius ** 2;
+      case "square": // Square
+        return shape.sideLength ** 2;
+      case "rectangle": // Rectangle
+        return shape.width * shape.height;
+      default:
+        throw new Error("Invalid shape kind");
+    }
+  }
+*/
+  type circle = {
+    kind: string,
+    radius: float,
+  }
+
+  type square = {
+    kind: string,
+    sideLength: float,
+  }
+
+  type rectangle = {
+    kind: string,
+    width: float,
+    height: float,
+  }
+
+  type shape =
+    | Circle(circle)
+    | Square(square)
+    | Rectangle(rectangle)
+
+  let area = (shape: shape): float => {
+    switch shape {
+    | Circle({radius}) => Js.Math._PI *. radius ** 2.
+    | Square({sideLength}) => sideLength ** 2.
+    | Rectangle({width, height}) => width *. height
+    }
+  }
+}