I am programming in scheme, here is my code:

$($define $($sum n$)$

$($if $($eq$?$n $0)$

$0$

$(+$n $($sum $(-$n $1)))))$

$($define $($ReverseEm elems$)$

$($if $($null$?$elems$)$

$\text{'}()$

$($append $($ReverseEm $($cdr elems$))$

$($list $($car elems$)))))$

$($define $($nonNegative num$)$

$($if $(>=$num $0)$

$$ num

$0))$

$($define $($JustDoIt elems$)$

$($if $($null$?$elems$)$

$\text{'}()$

$($cons $($nonNegative $($car elems$))($JustDoIt $($cdr elems$)))))$