Handle argument evaluation

lib/include/am.h

@@ -7,7 +7,7 @@
 #define AM_STACK_SIZE 128U
 
 typedef struct am {
-	expr_t *argl, *env, *expr, *val;
+	expr_t *argl, *env, *expr, *unev, *val;
 	expr_t **sp, *stack[AM_STACK_SIZE];
 	store_t store;
 } am_t;