define program
    [number]
end define

function main
    replace [program]
        p [number]
    by
        p [fact][fact0]
end function

function fact
    replace [number]
       n [number]
    construct nMinusOne [number]
       n [- 1]
    where 
       n [> 1]
    construct factMinusOne [number]
       nMinusOne [fact]
    by
       n [* factMinusOne]
end function 
       
function fact0
  replace [number]
       0
  by
       1
end function