Fix learn page exercise and add unit tests (93)

- Fix Validate Data exercise solution: add parentheses around pipe
  expression to resolve operator precedence issue
- Add unit tests for all 7 exercise solutions to prevent future
  regressions

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: claude

.claude/tasks/done/93-check-learn-exercices.md

@@ -0,0 +1,15 @@
+## Problem to solve
+
+At least the solution of the last exercice does not parse.
+
+```elo
+let Product = { name: String, price: Int } in
+  assert({ name: 'Widget', price: '99' } |> Product == { name: 'Widget', price: 99 })
+```
+
+## Idea
+
+* Check the unit test we have that was supposed to check all examples/exercices on
+  the website is up to date.
+* Complete it if needed
+* Fix examples that don't work (or fix parser/compilation to make them pass)

test/unit/learn-examples.unit.test.ts

@@ -168,3 +168,51 @@ describe('Learn Page Examples - Lesson 15: Parsing Data', () => {
     assert.throws(() => compile("Int('not a number')", { runtime }), /expected Int/);
   });
 });
+
+/**
+ * Exercise Solutions
+ * These tests verify that all exercise solutions on the Learn page
+ * are valid Elo code that compiles and evaluates successfully.
+ */
+
+describe('Learn Page Exercises - Build a Greeting', () => {
+  it('should pass the greeting assertion', () => {
+    assert.strictEqual(compile("assert('Hello, ' + 'World!' == 'Hello, World!')", { runtime }), true);
+  });
+});
+
+describe('Learn Page Exercises - Product Total', () => {
+  it('should pass the product total assertion', () => {
+    assert.strictEqual(compile("assert({ price: 25, quantity: 4 }.price * { price: 25, quantity: 4 }.quantity == 100)", { runtime }), true);
+  });
+});
+
+describe('Learn Page Exercises - Text Transform', () => {
+  it('should pass the text transform assertion', () => {
+    assert.strictEqual(compile("assert(upper(trim('  hello  ')) == 'HELLO')", { runtime }), true);
+  });
+});
+
+describe('Learn Page Exercises - Rectangle Area', () => {
+  it('should pass the rectangle area assertion', () => {
+    assert.strictEqual(compile("let width = 8, height = 5 in assert(width * height == 40)", { runtime }), true);
+  });
+});
+
+describe('Learn Page Exercises - Filter and Double', () => {
+  it('should pass the filter and double assertion', () => {
+    assert.strictEqual(compile("assert(([5, 12, 8, 20, 3, 15] |> filter(x ~> x > 10) |> map(x ~> x * 2)) == [24, 40, 30])", { runtime }), true);
+  });
+});
+
+describe('Learn Page Exercises - Order Total', () => {
+  it('should pass the order total assertion', () => {
+    assert.strictEqual(compile("let order = { price: 50, quantity: 3 } in assert(order.price * order.quantity == 150)", { runtime }), true);
+  });
+});
+
+describe('Learn Page Exercises - Validate Data', () => {
+  it('should pass the validate data assertion', () => {
+    assert.strictEqual(compile("let Product = { name: String, price: Int } in assert(({ name: 'Widget', price: '99' } |> Product) == { name: 'Widget', price: 99 })", { runtime }), true);
+  });
+});

web/src/pages/learn.astro

@@ -732,7 +732,7 @@ in
           <h4>Solution</h4>
           <div class="lesson-example" data-action="click->doc#tryExample">
             <pre class="example-code">let Product = &#123; name: String, price: Int &#125; in
-  assert(&#123; name: 'Widget', price: '99' &#125; |> Product == &#123; name: 'Widget', price: 99 &#125;)</pre>
+  assert((&#123; name: 'Widget', price: '99' &#125; |> Product) == &#123; name: 'Widget', price: 99 &#125;)</pre>
           </div>
         </div>
       </section>