It works, basic but works, need to move out logic to places, like ASTNode array shouldn't be on the lexer or future logic for fractions and error handling in the evaluator. Just the things at the top of my head

include/parser.h

@@ -1,3 +1,6 @@
+#ifndef PARSER_H
+#define PARSER_H
+
 #include "lexer.h"
 #include <stdint.h>
 
@@ -23,3 +26,4 @@ uint8_t node_rbp(ASTNode node);
 AST parse(ASTNodeArray *arr);
 ASTNode *parse_expr(ASTNodeSlice *slice, uint8_t min_bp);
 
+#endif // !PARSER_H