factorial/ ( n k -- n!/k! )

Vocabulary

math.factorials

Inputs

n	an object
k	an object

Outputs

n!/k!

an object

Definition

USING: combinators kernel math ranges sequences ;

IN: math.factorials

: factorial/ ( n k -- n!/k! )
    {
        { [ dup 1 <= ] [ drop factorial ] }
        { [ over 1 <= ] [ nip factorial recip ] }
        [
            2dup < [ t ] [ swap f ] if [ (a..b] product ] dip
            [ recip ] when
        ]
    } cond ;