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/interpreter.h

@@ -0,0 +1,26 @@
+#ifndef INTERPRETER_H
+#define INTERPRETER_H
+
+#include "expr.h"
+#include "token.h"
+
+typedef enum {
+    INS_STRING,
+    INS_DOUBLE,
+    INS_BOOLEAN,
+    INS_NULL
+} ObjectInstanceType;
+
+typedef struct Object {
+    ObjectInstanceType instance;
+    union {
+        char* string;
+        double number;
+        int boolean;
+    } value;
+} Object;
+
+void Interpret(Expr*);
+void FreeObject(Object*);
+
+#endif