fix typo

interpreter/thunk.c

@@ -49,7 +49,7 @@ double readR(Thunk* thunk) {
     assert(thunk != NULL);
     
     if (thunk->desc != (Desc*) __REAL__) {
-        printf("readC: not a real: ");
+        printf("readR: not a real: ");
         printDesc(thunk->desc);
         exit(-1);
     }