alternating-factorial ( n -- m )

Vocabulary

math.factorials

Inputs

n

an object

Outputs

m

an object

Definition

USING: kernel math ranges sequences ;

IN: math.factorials

: alternating-factorial ( n -- m )
    dup 1 > [
        [ [1..b] ] keep even? [ [ odd? ] ] dip [ = ] curry
        compose [ [ [ factorial ] ] ] dip
        [ bi [ neg ] when ] curry compose map-sum
    ] [ drop 1 ] if ;