S-algol

! -----------------------------------------------------------------------------
! 
! Towers of Hanoi
! 
! -----------------------------------------------------------------------------

let read.a.disc = proc( string s -> int )
begin
    write "type number of discs for ", s, ": "
    let d = readi
    if d < 0 or d > 10 do
    begin
        write "number must be in range 0..10\n"
        0
    end
    else d
end

let hanoi = proc( int n, from, to, using )
! move n discs from tower 'from' to tower 'to' using tower 'using'
begin
    if n > 0 do
    begin
        hanoi( n - 1, from, using, to )
        write n, " from ", from, " to ", to, "\n"
        hanoi( n - 1, using, to, from )
    end
end

let discs = read.a.disc( "Hanoi" )
if discs ~= 0 do hanoi( discs, 1, 3, 2 )