Updated the project structure, and modified the Makefile to hopefully be future proof so I can freely make sub-folders in the src/ folder and not have to worry about breaking the Makefile.

src/parser.h

@@ -0,0 +1,15 @@
+#ifndef PARSER_H
+#define PARSER_H
+
+#include "expr.h"
+#include "scanner.h"
+#include "token.h"
+#include <stdarg.h>
+#include <stdlib.h>
+#include <string.h>
+
+Expr* GenerateExpressionTree(const TokenList* list);
+void PrintExpressionTree(const Expr*);
+void FreeExpressionTree(Expr*);
+
+#endif