There is a misguide in documentation:

This function is obviously expected to return 4 (as the first line in the screenshot says) but the function name (definitely_not_4) is misleading:

definitely_not_4 = x ->
    x + 2
    4

print <|  definitely_not_4 40  #=> not 4

and it definitely returns 4:

...in contrast with the function name.