fixes #915

xml/chapter4/section1/subsection2.xml

@@ -2140,6 +2140,56 @@ list("logical_composition",
     as derived components.
       </JAVASCRIPT>
     </SPLIT>
+    <SOLUTION>
+      GitHub user EmilyOng provides a solution for the alternative:
+      how to implement 
+      <JAVASCRIPTINLINE>&amp;&amp;</JAVASCRIPTINLINE> and
+      <JAVASCRIPTINLINE>||</JAVASCRIPTINLINE>
+      as derived components.
+      <SNIPPET>
+	<JAVASCRIPT>
+function make_conditional_expr_decl(predicate, consequent_expression, alternative_expression) {
+    return list("conditional_expression", predicate, consequent_expression, alternative_expression);
+}
+function make_literal(value) {
+    return list("literal", value);
+}
+
+// Syntax selectors
+function logical_operation(component) {
+    return head(tail(component));
+}
+function first_expression(component) {
+    return head(tail(tail(component)));
+}
+function second_expression(component) {
+    return head(tail(tail(tail(component))));
+}
+
+function logical_comp_decl_to_conditional_expr_decl(component) {
+    const operation = logical_operation(component);
+
+    return operation === "&amp;&amp;"
+        ? make_conditional_expr_decl(
+            first_expression(component),
+            second_expression(component),
+            false
+        )
+        : operation === "||"
+        ? make_conditional_expr_decl(
+            first_expression(component),
+            true,
+            second_expression(component)
+        )
+        : error(component, "unknown operation -- logical_comp_decl_to_conditional_expr_decl");
+}
+
+display(logical_comp_decl_to_conditional_expr_decl(parse("a &amp;&amp; b;")));
+display(logical_comp_decl_to_conditional_expr_decl(parse("a || b;")));
+display(logical_comp_decl_to_conditional_expr_decl(parse("(a &amp;&amp; !b) || (!a &amp;&amp; b);")));
+	</JAVASCRIPT>
+      </SNIPPET>
+    </SOLUTION>
   </EXERCISE>
 
   <EXERCISE>