get "libhdr"
static $( randstate = ? $)

let rand() = valof
$(  randstate := random(randstate)
    resultis randstate >> 7
$)

let showboard(size, board, goal) be
$(  writes(" == BOARD == ")
    for i=1 to 19 do wrch(' ')
    writes(" == GOAL ==*N")

    for i=1 to 2
    $(  writes("  ")
        for j=1 to size do writef(" %N",j)
        test i=1 for j=1 to 30-2*size do wrch(' ') or wrch('*N')
    $)

    for row=0 to size-1 for i=1 to 2
    $(  writef("%C.", 'A'+row)
        for col=0 to size-1 do
            writef(" %N", (i=1->board,goal)!(row*size+col))
        test i=1 for j=1 to 30-2*size do wrch(' ') or wrch('*N')
    $)
$)

let readmove(size) = valof
$(  let ch = ? and x = ?
    writes("Enter row or column, or Q to quit: ")
    ch := rdch()
    unless ch = '*N' x := rdch() repeatuntil x = '*N'
    ch := ch | 32;
    if ch = 'q' | ch = endstreamch finish
    if 0 <= (ch-'1') < size | 0 <= (ch-'a') < size resultis ch
$) repeat

let flip(size, board, n, col) be
    test col
        do flipcol(size, board, n)
        or fliprow(size, board, n)
and flipcol(size, board, n) be
    for i=0 to size-1 do
        board!(i*size+n) := 1-board!(i*size+n)
and fliprow(size, board, n) be
    for i=0 to size-1 do
        board!(n*size+i) := 1-board!(n*size+i)

let makegoal(size, goal) be
    for i=0 to size*size-1 do goal!i := rand() & 1

let makeboard(size, board, goal) be
$(  for i=0 to size*size-1 do board!i := goal!i
    for i=0 to 10+2*(rand() & 15) do
        flip(size, board, rand() rem size, rand() & 1)
$)

let win(size, board, goal) = valof
$(  for i=0 to size*size-1
        unless board!i = goal!i resultis false
    resultis true
$)

let play(size, board, goal) be
$(  let moves = 0 and move = ?
    $(  showboard(size, board, goal)
        wrch('*N')
        if win(size, board, goal)
        $(  writef("You won in %N moves!*N", moves)
            return
        $)
        moves := moves + 1
        move := readmove(size)
        test '0' <= move <= '9'
            do flipcol(size, board, move-'1')
            or fliprow(size, board, move-'a')
    $) repeat
$)

let start() be
$(  let board = vec 63 and goal = vec 63
    let size = ?
    writef("****** FLIP THE BITS *******N")
    $(  writef("Size (3-8)? ")
        size := readn()
    $) repeatuntil 3 <= size <= 8
    writef("Random number seed? ")
    randstate := readn()
    wrch('*N')
    makegoal(size, goal)
    makeboard(size, board, goal)
    play(size, board, goal)
$)