From @AlexDaniel

Code​:
say combinations 2, 0.5

Result​:
(())

Code​:
say combinations 2, 1.5

Result​:
This type cannot unbox to a native integer
  in block <unit> at -e line 1

These results are inconsistent. 0.5 cannot be unboxed to a native int too, but it is accepted. I think that both should result in the same error.

From @usev6

The implementation has changed with rakudo commit f220a5ed so that Int() is called on $k (and $n).

The examples work consistently now, but it looks like there are no tests for this in roast​:

$ perl6-m -e 'say combinations 2, 0.5'
(())

$ perl6-m -e 'say combinations 2, 1.5'
((0) (1))

$ perl6-m -e 'say combinations 4, 2.5'
((0 1) (0 2) (0 3) (1 2) (1 3) (2 3))

@usev6 - Status changed from 'new' to 'open'

From @zoffixznet

Tests added​: Raku/roast@0ff33b312b

@zoffixznet - Status changed from 'open' to 'resolved'