lisp.aat

extern fn printf str, ... -> i32
extern fn malloc i32 -> u8*
extern fn strlen str -> i32

rec Parser(pos: i32, text: str, len: i32)

fn peek parser: &Parser -> char = parser.text[parser.pos]

fn consume parser: &Parser = parser.pos = parser.pos + 1

fn eof parser: &Parser -> bool =
    if ret parser.pos >= parser.len then true
    else false

fn isDigit c: char -> bool =
    if ret c >= '0' && c <= '9' then true
    else false

fn isChar parser: &Parser, c: char -> bool =
    if ret (peek &parser) == c then true
    else false

fn print b: bool = {
    if b == true then printf "true"
    else printf "false"
}

fn parseNumber parser: &Parser -> i32 = {
    var accum = 0
    val zero = '0' as i32

    while (isDigit peek &parser) {
        accum = accum * 10
        accum = accum + (peek &parser) as i32 - zero
        consume &parser
    }

    accum
}

type lispType = Int i32 | Bool bool | Error | Nil | Cons lispType*, lispType* | Char char


fn parse parser: &Parser -> lispType = {
    if isDigit peek &parser
        ret Int parseNumber &parser
    if isChar &parser, '(' {
        consume &parser
        if isChar &parser, ')' {
            consume &parser
            ret Nil ()
        }
        ret Error ()
    } 
    if isChar &parser, '#' {
        consume &parser
        if isChar &parser, 't' {
            consume &parser
            ret Bool true
        }
        if isChar &parser, 'f' {
            consume &parser
            ret Bool false
        }
        if isChar &parser, '\\' {
            consume &parser
            val c = peek &parser
            ret Char c
        }
        ret Error ()
    }
    Error ()
}

fn print ty: lispType = {
    if ty is Int
        printf "%i", ty.0
    if ty is Nil
        printf "()"
    if ty is Bool
        if ty.0 == true
            printf "#t"
        else
            printf "#f"
    if ty is Char
        printf "#\\%c", ty.0
}

@entry
fn main() -> () = {
    val text = "#\\a"
    var parser = Parser {
        pos: 0,
        text: text,
        len: strlen text,
    }

    print parse &parser
}