PicoLisp is built to be simple from the bottom-up. The author first designed a virtual machine architecture. This allows for simplicity to be baked into the language. To emphasize simplicity, PicoLisp only has one single data structure, the cell. All higher level data types, numbers, symbols, and lists, are built from cells.
We’ll start with a simple game - represented with a cell - and use some numbers and symbols. Perhaps we can use lists when writing messages to the player. The game is… actually its a number guessing AI. You’ll think of a number, and by answering simple questions, the program will either guess your number, or know you cheated!
How can we represent this game with a cell? Well, the boundaries for this game are two numbers your number is between. We can create a cell to represent those boundaries and us a symbol to point to it with a name like this:
(set '*Bounds '(1 . 100))Actually, I just realized we’re already using lists, this is Lisp
after all! List processing is what it is all about. Everything in
the parenthesis above is a list. The PicoLisp interpreter knows how
to read lists like that as a program. We can read it too. That list
starts with set which is a PicoLisp function that lets you set
the value or val of a symbol. So, following set is the
symbol whose value you want to set. Now, there’s something special
here… the ' mark. This is a shorthand for the quote function
which marks something as a piece of data, rather than something the
PicoLisp reader should evaluate. Without that quote, *Bounds would
evaluate to NIL and NIL is a protected symbol:
: (set *Foo 1)
!? (set *Foo 1)
NIL -- Protected symbolBad things would happen if we could set the value of NIL. So,
we’re setting the value of the symbol *Bounds to another quoted
list. This is our cell. The dot in between 1 and 100 is one way
to link these two numbers into a cell. We put 1 in the car of
the cell and 100 in the cdr (pronounced “could’r”) by using
that dot to indicate the cell. We could also construct a cell
by using the cons function:
: (cons 1 100)
-> (1 . 100)So now, if you type *Bounds at the repl, it should return its
value, (1 . 100). There. That is all the data we need to represent
our guessing game.
(set '*Bounds '(1 . 100))
(de small () (car *Bounds))
(de big () (cdr *Bounds))
(de guess-my-number ()
(if (> (small) (big))
(cheater)
(>> 1 (+ (small) (big))) ) )
(de smaller ()
(set '*Bounds (cons (small) (dec (guess-my-number))))
(guess-my-number) )
(de bigger ()
(set '*Bounds (cons (inc (guess-my-number)) (big)))
(guess-my-number) )
(de cheater ()
(prinl '(You " " cheated!))
(new-game) )
(de new-game (S B)
(set '*Bounds (cons (or S 1) (or B 100)))
(go) )
(de go ()
(prinl (text "Think of a number between @1 and @2!" (small) (big)))
(wait 2000)
(prinl "Here we go! My first guess is... ")
(guess-my-number) )(+ 2 2)
(de boo () (print "boom shsks"))(boo)
(boo)Just realized that even without docs hooked up to the emacs system, having the
pil repl and org babel might help me build another presentation of docs as go
through. lets see..
(help 'help T)This needs to have the babel interpreter using debug mode to work properly, and the way it outputs the result has all the non printing characters sent through the repl. Probably needs some help developing picolisp mode further.