can now parse prefix expressions!

src/ast/expressions/prefix.cpp

@@ -0,0 +1,19 @@
+#include "prefix.hpp"
+
+#include "token/token.hpp"
+
+namespace ast {
+
+    prefix_expr::prefix_expr(token::token token, std::string op)
+        : token(std::move(token)),
+          op(op),
+          right(nullptr) {}
+
+    std::string prefix_expr::token_literal() const {
+        return token.literal;
+    }
+
+    std::string prefix_expr::str() const {
+        return token.literal + right->str();
+    }
+} // namespace ast