feat: code generation for conditional and switch statements

src/Ast.zig

@@ -104,7 +104,7 @@ pub const Node = struct {
         },
         switch_stmt: struct {
             condition_expr: ?*Node,
-            cases: ?[]*Node,
+            cases: []*Node,
         },
         knot_decl: struct {
             prototype: *Node,
@@ -175,7 +175,7 @@ pub const Node = struct {
         tag: Tag,
         loc: Span,
         condition_expr: ?*Node,
-        cases_list: ?[]*Node,
+        cases_list: []*Node,
     ) !*Node {
         const node = try Node.create(gpa, tag, loc);
         node.data = .{
@@ -227,6 +227,10 @@ pub const Error = struct {
         invalid_lvalue,
         too_many_arguments,
         too_many_parameters,
+
+        invalid_else_stmt,
+        unexpected_else_stmt,
+        invalid_switch_case,
     };
 };