Slot Machines

Playing slot machines can be pretty fun, but don't be fooled by claims that the casino has the "loosest slots", odds are probably still against you. I thought it would be fun (and cheaper!) to build a slot machine simulator using Factor.

Our slot machine is going to be a console application that will look something like this:

Spinning

Even though our slot machine is text-only, we can still make use of some nice unicode characters to be our symbols:

CONSTANT: SYMBOLS "☀☁☂☃"

Each spin chooses a different symbol at random (each being equally likely):

: spin ( value -- value' )
    SYMBOLS remove random ;

To reproduce the feel of spinning a slot machine, we will introduce a slight delay so that the wheel spins fast at the beginning and then slower and slower until it stops on a symbol:

: spin-delay ( n -- )
    15 * 25 + milliseconds sleep ;

Spinning the slot machine takes a spin number, delays for a bit, then rotates each wheel (we stop spinning the first column after 10 spins, the second after 15, and the last after 20):

: spin-slots ( a b c n -- a b c )
    {
        [ spin-delay ]
        [ 10 < [ [ spin ] 2dip ] when ]
        [ 15 < [ [ spin ]  dip ] when ]
        [ drop spin ]
    } cleave ;

Display

Each "spin" of the slot machine will be printed out. Using ANSI escape sequences, we move the cursor to the top left ("0,0") of the screen and then issue a clear screen instruction. Then we print out the current display and flush the output to screen:

: print-spin ( a b c -- a b c )
    "\e[0;0H\e[2J" write
    "Welcome to the Factor slot machine!" print nl
    "  +--------+" print
    "  | CASINO |" print
    "  |--------| *" print
    3dup "  |%c |%c |%c | |\n" printf
    "  |--------|/" print
    "  |    [_] |" print
    "  +--------+" print flush ;

Playing

The player will have won if, after all the spins, the "pay line" shows three of the same characters:

: winner? ( a b c -- )
    3array all-equal? nl "You WIN!" "You LOSE!" ? print nl ;

Playing the slot machine consists of spinning the wheels 20 times, displaying each spin to the user, then checking if the user has won the game.

: play-slots ( -- )
    f f f 20 iota [ spin-slots print-spin ] each winner? ;

Since our casino wants the user to keep playing, we make it really easy to just hit ENTER to continue:

: continue? ( -- ? )
    "Press ENTER to play again." write flush readln ;

And, to finish it off, we define a "MAIN" entry point that will be run when the script is executed:

: main-slots ( -- )
    [ play-slots continue? ] loop ;

MAIN: main-slots

The code for this is on my Github.