Fix append of VoidValue

core/src/main/kotlin/eu/iamgio/quarkdown/function/expression/visitor/AppendExpressionVisitor.kt

@@ -41,6 +41,22 @@ import eu.iamgio.quarkdown.function.value.VoidValue
  * These two values are then joined together by this [AppendExpressionVisitor], producing:
  * `StringValue(three plus two is 5)`
  *
+ * The same principle applies to 'block expressions':
+ * ```
+ * .if {...}
+ *     Item 1
+ *     .foreach {2..4}
+ *         n:
+ *         Item .n
+ *     Item 5
+ * ```
+ * The previous example contains a body composed of multiple expressions:
+ * - `StringValue(Item 1)`;
+ * - `FunctionCall(foreach)` which returns an `IterableValue` of 3 elements;
+ * - `StringValue(Item 5)`.
+ * After appending these values, the resulting expression is an `IterableValue` (a [GeneralCollectionValue] in particular)
+ * which contains: `Item 1`, `Item 2`, `Item 3`, `Item 4`, `Item 5`.
+ *
  * @param other expression to append to the visited expression
  * @see ComposedExpression
  */
@@ -51,6 +67,10 @@ class AppendExpressionVisitor(private val other: Expression) : ExpressionVisitor
     private fun Value<*>.concatenate(): InputValue<*> {
         val otherEval = other.eval() // Evaluate the next expression.
 
+        // Void values are ignored.
+        if (this is VoidValue) return otherEval as InputValue<*>
+        if (otherEval is VoidValue) return this as InputValue<*>
+
         // If the other value is a collection, add the current value to it as the first element.
         if (otherEval is IterableValue<*> && this is OutputValue<*>) {
             return GeneralCollectionValue(listOf(this, *otherEval.unwrappedValue.toList().toTypedArray()))

test/src/test/kotlin/eu/iamgio/quarkdown/test/FullPipelineTest.kt

@@ -235,6 +235,20 @@ class FullPipelineTest {
         assertFailsWith<InvalidArgumentCountException> {
             execute(".function {hello}\n   target:\n  `Hello` .target!\n\n.hello") {}
         }
+
+        execute(
+            """
+            .if {yes}
+                .function {hello}
+                    name:
+                    Hello, *.name*!
+                
+                # .hello {world}
+                .hello {iamgio}
+            """.trimIndent(),
+        ) {
+            assertEquals("<h1>Hello, <em>world</em>!</h1><p>Hello, <em>iamgio</em>!</p>", it)
+        }
     }
 
     @Test
@@ -253,6 +267,18 @@ class FullPipelineTest {
         ) {
             assertEquals("<p>Hello</p>", it)
         }
+
+        execute(
+            """
+            .var {x} {no}
+            .if {.x}
+                Hi
+            .ifnot {.x}
+                Hello
+            """.trimIndent(),
+        ) {
+            assertEquals("<p>Hello</p>", it)
+        }
     }
 
     @Test