feat(furc/parser): add if expression

furc/include/furc/front/ast.hpp

@@ -137,6 +137,7 @@ public:
         Group,
         BinaryOp,
         UnaryOp,
+        If,
     };
 public:
     category_e category() const override { return ast_node_cat::Expression; }
@@ -214,6 +215,14 @@ struct unary_op_expr_node final : public expr_node {
     unary_op_type type = Positive;
 };
 
+struct if_expr_node final : public expr_node {
+    expr_type_e expr_type() const override { return If; }
+
+    expr_node* cond     = nullptr;
+    expr_node* thenExpr = nullptr;
+    expr_node* elseExpr = nullptr;
+};
+
 class lit_node : public expr_node {
 public:
     enum lit_type_e {

furc/src/front/parser.cpp

@@ -169,7 +169,7 @@ comp_stmt_node parser::parse_comp() {
 }
 
 expr_node* parser::parse_expr_primary() {
-    auto token = eat_token(token::Identifier, token::LParen, token::Integer, token::Char);
+    auto token = eat_token(token::Identifier, token::LParen, token::If, token::Integer, token::Char);
     switch (token.type) {
     case token::Identifier: {
         return m_arena->allocate<var_read_expr_node>(std::string(token.value.string));
@@ -180,6 +180,16 @@ expr_node* parser::parse_expr_primary() {
         eat_token(token::RParen);
         return m_arena->allocate<group_expr_node>(std::move(group));
     }
+    case token::If: {
+        if_expr_node ifExpr;
+        eat_token(token::LParen);
+        ifExpr.cond = parse_expr();
+        eat_token(token::RParen);
+        ifExpr.thenExpr = parse_expr();
+        eat_token(token::Else);
+        ifExpr.elseExpr = parse_expr();
+        return m_arena->allocate<if_expr_node>(std::move(ifExpr));
+    }
     case token::Integer: {
         return m_arena->allocate<int_lit_node>(int_lit_node(token.value.integer));
     }

furc/src/main.cpp

@@ -8,8 +8,7 @@ int main(void) {
     std::string_view content = R"(
         func main(argc: u64) -> s32 pre(arc > 1) {
             x: s32 = 1 + 2 * 3;
-            if (x == 9) return 1;
+            return if (x == 9) 1 else 0;
-            else return 0;
         }
     )";