slurp so many?

[ToddAndMargo via perl6-users]

Hi All,

I use `slurp` all the time, so of course, I can't
make heads or tails out of

     https://docs.perl6.org/routine/slurp

I want to slurp the first 400 characters of
a file and close the handle.  Am I missing a
`so many` parameter somewhere?

Many thanks,
-T