Double factorial is interpreted as the factorial function twice

[haykam821]

The double factorial, expressed as n‼, is instead interpreted as (n!)!. Wolfram Alpha interprets the following expressions correctly:

> 4!
24 # correct
> (4!)!
620448401733239439360000 # correct
> 4!!
620448401733239439360000 # expected 8
> 4‼
Error: unexpected character '‼' # expected 8; note that this is the double exclamation mark character U+203C

[printfn]

Thanks for the issue, I agree it would be good to fix this.