Fix examples so all ten parse

- 03: handler clause uses the canonical arrow (↯e ⟹ …, was ↯e ⇒ …)
- 05: give sin/cos a real placeholder body (⊥) — a comment-only body is
  empty and cannot parse
- Run parseExamples on the test runtime classpath; ParseExamples lives in
  the test source set and was never found on main.runtimeClasspath

./gradlew parseExamples now reports 10/10 PASS

build.gradle

@@ -47,8 +47,10 @@ test {
     }
 }
 
-task parseExamples(type: JavaExec, dependsOn: classes) {
+// ParseExamples lives in the test source set, so the task needs the test
+// runtime classpath (with main.runtimeClasspath the class was never found).
+task parseExamples(type: JavaExec, dependsOn: testClasses) {
     mainClass = 'com.mpl.test.ParseExamples'
-    classpath = sourceSets.main.runtimeClasspath
+    classpath = sourceSets.test.runtimeClasspath
     args = ['examples']
 }

examples/03_file_processing.mpl

@@ -4,4 +4,4 @@ processFile ≜ λpath: {
     result ← transform(data);
     writeFile(result, 🖫"output.txt");
     ⟨"success"|"failed"⟩
-} ↴ {↯e ⇒ ⟨⊥|e⟩};
+} ↴ {↯e ⟹ ⟨⊥|e⟩};

examples/05_module_definition.mpl

@@ -1,8 +1,8 @@
 -- Module definition example
 𝓜 Mathematics ⇒ {
     π ≜ 3.14159;
-    sin ≜ λx∈ℝ: {- implementation -};
+    sin ≜ λx∈ℝ: ⊥ {- implementation deferred until MPL executes -};
-    cos ≜ λx∈ℝ: {- implementation -}
+    cos ≜ λx∈ℝ: ⊥ {- implementation deferred until MPL executes -}
 };
 
 angle ← π/4;