chore: flat out the file structure

include/furvm/constant.hpp

@@ -0,0 +1,31 @@
+#ifndef FURVM_CONSTANT_HPP
+#define FURVM_CONSTANT_HPP
+
+#include "furvm/fwd.hpp"
+
+#include <cstdint>
+#include <string_view>
+
+namespace furvm {
+
+// TODO: Array constants
+struct constant {
+    enum type_e {
+        S32 = 0,
+        U32,
+        S64,
+        U64,
+        String,
+    } type = S32;
+    union {
+        std::int32_t     s32;
+        std::uint32_t    u32;
+        std::int64_t     s64;
+        std::uint64_t    u64;
+        std::string_view string;
+    };
+};
+
+} // namespace furvm
+
+#endif // FURVM_CONSTANT_HPP