invalid type casting on interface

[ltzmaxwell]

Description

the code should produce the following error: ./prog.go:14:18: cannot convert a (variable of interface type Runner) to type Swimmer: Runner does not implement Swimmer (missing method Swim)

But it works fine in Gno.

package main

type Runner interface {
	Run()
}

type Swimmer interface {
	Swim()
}

func main() {
	a := Runner(nil)
	println(interface{}(a))
	println(Swimmer(a))
}

Output:
undefined
undefined