Pico8lisp is a small lisp interpreter built on PICO-8 virtual machine!

The shell is currently inflexible. Parse errors typically crash or exhaust memory. If your environment crashes, reload the page to reset.

Try out Pico8Lisp on the Pico8 Website here

You can type commands directly into the shell.

> (+ 1 2)
  3

<return> submits the command.

Press <up> and <down> to scroll through your command history.

Press <left> and <right> to move the cursor.

<backspace> will remove the character to the left of the cursor.

<shift>-d will remove the character to the right of the cursor.

Toggle between insert and replace modes by pressing <shift>-I.

Literal numbers are just the numbers themselves.

> 123
  123

Symbols are used as names for forms/functions/constants/just about anything. Symbols can be written as series of letters a-z. More on that later.

Nil can be written as nil

> nil
  ()

Note that nil evaluated to an empty list (). That's because the symbol nil is bound to the empty list. This is the only false value in picolisp!

Everything except nil is true. But we do have a special value to represent truth.

> $t
  $t

The first element of a list is assumed to be a function.

> (+ 1 2)
  3

You can even nest list expressions.

> (+ (+ 1 2) 3)
  6

Supported Numeric Functions

• + plus
• - subtract
• * multiply
• / divide
• % modulus

If your repl gets confusing, clear the screen

(clear)

You can write a list literal with the quote function.

> (quote (1 2 3))
  (1 2 3)

Quote prevents the list from being evaluated!

There is a special quote operator to make this to read.

> '(1 2 3)
  '(1 2 3)

There are many functions which work with lists

> (empty? ())
  $t
> (len '(1 2 3))
  3
> (first '(1 2 3))
  1
> (second '(1 2 3))
  2
> (nth 2 '(1 2 3))
  3
> (rest '(1 2 3))
  (2 3)
> (reverse '(1 2 3))
  (3 2 1)
> (reduce + 0 '(1 2 3 4))
  10
> (map inc '(1 2 3))
  (2 3 4)
> (filter even? '(1 2 3 4))
  (2 4)

By default symbols are evaluated, but you can prevent that with quote.

> 'mysymbol
  mysymbol

You can define global symbols with a value.

> (def age 38)
  38

> age
  38

While def symbols are globally available, you can make locally scoped definitions with let

> (let (x 3 y 2) (+ x y))
  5

Use defn to make a function globally accessible.

> (defn inc (x) (+ x 1))
  (fn (x) (+ x 1))

> (inc 2)
  3

Branches are supported by if statements.

> (if (= 1 1) 'happy 'sad)
  happy
> (if (= 1 2) 'happy 'sad)
  sad

If else if..., else statements are supported via cond

> (def x 1)
> (cond (= x 0) 'zero (= x 1) 'one $t 'other)
  one

Supported logic operators:

• = equals check
• > >= greater than (equals) numbers only
• < <= less than (equals) numbers only
• ! not
• and logical and
• or logical or
• ``

Predicates, functions which return true or false, typically end in a ?.

• even?
• odd?

Examples

> (= 1 1)
  $t
> (> 1 2)
  ()
> (= '(1 2) '(1 2))
  $t
> (! nil)
  $t
> (! $t)
  nil
> (! 1)
  nil
`> (and nil 1)
  ()
> (or nil 1)
  $t

This work is licensed under a Creative Commons Attribution 4.0 International License.