fix print thunk bug (interference with the GC)

interpreter/thunk.c

@@ -101,13 +101,19 @@ void print(bool force) {
     } else {
         int arity = printDesc(thunk->desc);
 
+        // Put the arguments on the stack before any "eval", otherwise GC
+        // may screws up the pointers
+        for (int i = 0; i < arity; i++) {
+            push_a(thunk->_args[arity-i-1]);
+        }
+        
         for (int i = 0; i < arity; i++) {
             printf(" ");
-            
-            push_a(thunk->_args[i]);
-            if (force) thunk->_args[i]->desc->eval();
+
+            if (force) peek_a()->desc->eval();
             print(force);
         }
+        
     }
 
     printf("]");