Lisp

A simple lisp-style interpreter made by someone who has never interacted with anything in the lisp language family.

Because of that, this is likely nothing like a "proper" lisp dialect.

The only thing close to research that I did was play around with my editor's (NeoVim) highlighting for ".lisp" files and found some keywords that were highlighted.

(eval
    (print "What is your age?\nAge: ")
    (let x (parseint (readline)))
    (println "You were born" x (if (!= x 1) "years" "year") "ago.")
)

Literals

• Strings - 'foo' and "foo"
• Integers - 123, 0b101, 0x123
• Boolean - true and false

Global Functions

• print - print values to stdout
• println - print with trailing newline
• parseint - parse string to int
• readline - read one line from stdin
• append - append value to array (returns new array)
• length - get length of array or string
• int, char, string, bool - cast value to given type

Operations

• - - Subtract (- 1 2 3) -> -4
• + - Add numbers / Concat strings (+ 1 2 "hello" true) -> 3hellotrue
• * - Multiply (* 2 3 4) -> 24
• / - Divide (/ 10 5) -> 2
• @ - Create array (@ 1 2 3)
• == - Equals
• != - Not Equals
• <, <= - Less than, less than or equal to
• >, >= - Greater than, greater than or equal to
• . - Index into array or string (. "hello" 0) -> 'h'

Variables

(let x)         ; declare variable x
(let y (+ 2 3)) ; declare variable x and assign to it
(= x (+ 3 10))  ; assign value to previously declared variable
(= y 1)         ; assign value to previously declared variable

User Functions

All user functions are anonymous. To be able to call them, they must be assigned to a variable.

(let foo (function param1 param2 body))

Example:

(eval
    (let foo (function x (
        if (- 5 x) (eval
            (println x)
            (foo (+ x 1))
        )
    )))
    (foo 0)
)

Conditionals

(if condition (then))
; and
(if condition (then) (else))

Loops

While Loops:

(while condition body)

Example:

(let i 0)
(while (< i (length a)) (eval
    (println (+ "a[" i "] =") (. a i))
    (= i (+ i 1))
))

For Loops:

(for init condition post body)

Example:

(for (let i 0) (< i (length a)) (= i (+ i 1)) (eval
    (println (+ "a[" i "] =") (. a i))
))