setvbuf can't make it unbuffered

[Nala Ginrut]

Hi guys!
I'm playing Guile 'cat' for Guile-100, but I found that 'setvbuf' seems
can't make it unbuffered.
Anyone folks could help it for me?

Here is the code:
https://gist.github.com/NalaGinrut/5151115