absprop gc_ptr(l:addr, a:t@ype)

typedef stack_t(a: t@ype+) = $extype "struct stack_t"

fun new {a:t@ype+}(&stack_t(a)? >> stack_t(a)) : void =
  "ext#"

fun {a:t@ype+} push(&stack_t(a) >> stack_t(a), a) : void =
  "ext#"

fun {a:t@ype+} pop(&stack_t(a) >> stack_t(a)) : Option(a) =
  "ext#"