PROGRAM free_fall
! example of strong typing
OPTION TYPO
PUBLIC y,v,a,g,t,dt,nshow    ! declare variables
LOCAL counter
CALL initial
CALL print_table
LET counter = 0
DO while y >= 0
   CALL Euler
   LET counter = counter + 1
   IF mod(counter,nshow) = 0 then
      CALL print_table
   END IF
LOOP
CALL print_table
END

SUB initial
    DECLARE PUBLIC y,v,a,g,t,dt
    LET t = 0
    LET y = 10
    LET v = 0
    LET g = 9.8
    LET a = -g
    LET dt = 0.01
END SUB

SUB Euler
    DECLARE PUBLIC y,v,a,g,t,dt
    LET y = y + v*dt
    LET a = -g
    LET v = v + a*dt
    LET t = t + dt
END SUB

SUB print_table
    DECLARE PUBLIC y,v,a,t,nshow
    IF t = 0 then
       INPUT prompt "number of time steps between output = ": nshow
       CLEAR       ! might want to omit this graphics statement
       PRINT "time (s)", "y (m)", "velocity (m/s)", "accel (m/s*s))"
       PRINT
    END IF
    PRINT t,y,v,a
END SUB