: SUM.OF.N.A ( N -- SUM[N] , calculate sum of N integers )
0 \ starting value of SUM
OVER 0> \ Is N greater than zero?
SWAP 1- SWAP \ decrement N
: SUM.OF.N.B ( N -- SUM[N] )
0 SWAP \ starting value of SUM
1+ 0 \ set indices for DO LOOP
?DO \ safer than DO if N=0
: SUM.OF.N.C ( N -- SUM[N] )
0 \ starting value of SUM
: SUM.OF.N.D ( N -- SUM[N] )
>R \ put NUM on return stack
0 \ starting value of SUM
: SUM.OF.N.E { NUM | SUM -- SUM[N] , use return stack }
NUM +-> SUM \ add NUM to SUM
-1 +-> NUM \ decrement NUM
: SUM.OF.N.F ( NUM -- SUM[N] , Gauss' method )