feat(furc/parser): add if statement

furc/include/furc/front/ast.hpp

@@ -52,6 +52,7 @@ public:
         Expression,
 
         Compound,
+        If,
     };
 public:
     category_e category() const override { return ast_node_cat::Statement; }
@@ -65,6 +66,16 @@ struct comp_stmt_node final : public stmt_node {
     std::vector<stmt_node*> stmts;
 };
 
+class expr_node;
+
+struct if_stmt_node final : public stmt_node {
+    stmt_type_e stmt_type() const override { return If; }
+
+    expr_node* cond       = nullptr;
+    stmt_node* thenBranch = nullptr;
+    stmt_node* elseBranch = nullptr;
+};
+
 class decl_node : public stmt_node {
 public:
     enum decl_type_e {

furc/src/front/parser.cpp

@@ -24,6 +24,19 @@ ast parser::parse() {
 stmt_node* parser::parse_stmt() {
     switch (m_lexer.peek_token().type) {
     case token::LBrace: return m_arena->allocate<comp_stmt_node>(parse_comp());
+    case token::If: {
+        m_lexer.next_token();
+        eat_token(token::LParen);
+        if_stmt_node node;
+        node.cond = parse_expr();
+        eat_token(token::RParen);
+        node.thenBranch = parse_stmt();
+        if (m_lexer.peek_token().type == token::Else) {
+            m_lexer.next_token();
+            node.elseBranch = parse_stmt();
+        }
+        return m_arena->allocate<if_stmt_node>(std::move(node));
+    }
     default: break;
     }