global n, rw, dd, ud

procedure main(args)
    n := integer(args[1]) | 8
    rw := list(n)
    dd := list(2*n-1)
    ud := list(2*n-1)
    solvequeen(1)
end

procedure solvequeen(c)
    if (c > n) then return show()
    else suspend placequeen(c) & solvequeen(c+1)
end

procedure placequeen(c)
    suspend (/rw[r := 1 to n] <- /dd[r+c-1] <- /ud[n+r-c] <- c)
end

procedure show()
    static count, line, border
    initial {
        count := 0
        line := repl("|   ",n) || "|"
        border := repl("----",n) || "-"
        }
    write("solution: ", count+:=1)
    write("  ", border)
    every line[4*(!rw - 1) + 3] <- "Q" do {
        write("  ", line)
        write("  ", border)
        }
    write()
    return      # Comment out to see all possible solutions
end