refactor(parser): change node handles to node results

Refs: #1

furc/src/main.cpp

@@ -7,7 +7,8 @@
 #include <iostream>
 
 int main(void) {
-    std::string               programStr = R"(
+    try {
+        std::string               programStr = R"(
     func main() {
         x = 5;
         x -= 3;
@@ -21,30 +22,36 @@ int main(void) {
         z = x + y;
     }
     )";
-    furc::front::parser       parser("<TEMP>", programStr);
-    furc::front::ir_generator generator;
+        furc::front::parser       parser("<TEMP>", programStr);
+        furc::front::ir_generator generator;
 
-    auto program = parser.parse();
-    if (program.has_error()) {
-        std::cerr << program << '\n';
-    }
-    program->accept(generator);
-
-    auto module = std::move(generator.move_module());
-    std::cout << "Generated IR:\n";
-    for (const auto& function : module.functions()) {
-        std::cout << function->name() << ":\n";
-        furlang::ir::block_index blockIndex = 0;
-        for (const auto& block : function->blocks()) {
-            std::cout << "  # block " << blockIndex++ << '\n';
-            for (const auto& instruction : block->instructions()) {
-                std::cout << "  " << *instruction << '\n';
-            }
-            std::cout << "  " << *block->exit() << '\n';
+        auto programResult = parser.parse();
+        if (programResult.has_error()) {
+            std::cerr << programResult.error() << '\n';
+            return 1;
         }
-    }
+        const auto& program = *programResult;
+        program->accept(generator);
 
-    return 0;
+        auto module = std::move(generator.move_module());
+        std::cout << "Generated IR:\n";
+        for (const auto& function : module.functions()) {
+            std::cout << function->name() << ":\n";
+            furlang::ir::block_index blockIndex = 0;
+            for (const auto& block : function->blocks()) {
+                std::cout << "  # block " << blockIndex++ << '\n';
+                for (const auto& instruction : block->instructions()) {
+                    std::cout << "  " << *instruction << '\n';
+                }
+                std::cout << "  " << *block->exit() << '\n';
+            }
+        }
+
+        return 0;
+    } catch (...) {
+        std::cerr << "Caught an exception in main!\n";
+        return 1;
+    }
 }
 
 #endif // LIBFURC