add parse and stringify

testbench/CMakeLists.txt

@@ -6,7 +6,6 @@ PRIVATE
     main.cpp
     yycc/constraint.cpp
     yycc/constraint/builder.cpp
-    yycc/string.cpp
     yycc/string/op.cpp
     yycc/string/reinterpret.cpp
 )

testbench/yycc/string.cpp

@@ -1,2 +0,0 @@
-
-namespace yycctest::string {}

testbench/yycc/string/op.cpp

@@ -48,12 +48,12 @@ namespace yycctest::string::op {
     }
 
     TEST(StringOp, Lower) {
-        auto rv = OP::lower(YYCC_U8("LOWER"));
+        auto rv = OP::to_lower(YYCC_U8("LOWER"));
         EXPECT_EQ(rv, YYCC_U8("lower"));
     }
 
     TEST(StringOp, Upper) {
-        auto rv = OP::upper(YYCC_U8("upper"));
+        auto rv = OP::to_upper(YYCC_U8("upper"));
         EXPECT_EQ(rv, YYCC_U8("UPPER"));
     }