100 REM FACTORIAL
110 DIM F(35): F(0)=1:  REM MEMOS
120 DIM S(35): SP=0:    REM STACK+PTR
130 FOR I=1 TO 13
140 : S(SP)=I: SP=SP+1: REM PUSH(I)
150 : GOSUB 200
160 : SP=SP-1:          REM POP
170 : PRINT I;"! = ";S(SP)
180 NEXT I
190 END
200 REM FACTORIAL: S(SP-1) = S(SP-1)!
210 IF F(S(SP-1)) THEN 240: REM MEMOIZED
220 S(SP)=S(SP-1)-1: SP=SP+1: GOSUB 200: REM RECURSE
230 SP=SP-1: F(S(SP-1))=S(SP-1)*S(SP): REM MEMOIZE
240 S(SP-1)=F(S(SP-1)): REM PUSH(RESULT)
250 RETURN