frustration/frustration.rs

use std::cmp;
use std::io;
use std::process;
use std::convert::TryInto;

//const CORE_SIZE: usize = 65280
const CORE_SIZE: usize = 128;

#[derive(Debug)]
enum State {
    Compiling,
    Interpreting
}

#[derive(Debug)]
struct Core {
    ram: [u8; CORE_SIZE],
    ip: u16,
    dp: u16,  // newest link field, or 0
    here: u16, // first unused byte
    state: State,
    dstack: [u16; 64],
    tds: usize,  // post-incremented; exceeds top by one
    rstack: [u16; 64],
    trs: usize,  // post-incremented; exceeds top by one
}

type Primitive = fn(&mut Core);

struct ShortName {
    bytes: [u8; 3],
    length: u8
}

fn truncate_name(name: &str) -> ShortName {
    let name_bytes = name.as_bytes();
    let mut out = ShortName {
        bytes: [32, 32, 32],
        length: std::cmp::min(3, name_bytes.len()) as u8 };
    out.bytes[0..out.length as usize].copy_from_slice(&name_bytes[0..out.length as usize]);
    return out;
}

struct TableEntry {
    f: Primitive,
    name: ShortName
}

// NOTE: lazy_static or SyncLazy would allow nicer init
const PRIMITIVES: [TableEntry; 8] = [
    TableEntry {f: ret  , name: ShortName {bytes: ['r' as u8, 'e' as u8, 't' as u8], length: 3}},
    TableEntry {f: dot  , name: ShortName {bytes: ['.' as u8, 32, 32], length: 1}},
    TableEntry {f: store, name: ShortName {bytes: ['!' as u8, 32, 32], length: 1}},
    TableEntry {f: load , name: ShortName {bytes: ['@' as u8, 32, 32], length: 1}},
    TableEntry {f: add  , name: ShortName {bytes: ['+' as u8, 32, 32], length: 1}},
    TableEntry {f: sub  , name: ShortName {bytes: ['-' as u8, 32, 32], length: 1}},
    TableEntry {f: mul  , name: ShortName {bytes: ['*' as u8, 32, 32], length: 1}},
    TableEntry {f: div  , name: ShortName {bytes: ['/' as u8, 32, 32], length: 1}}
];

fn new_core() -> Core {
    let mut c = Core {
        ram: [0; CORE_SIZE], ip: 0, dp: 0, here: 2, state: State::Interpreting,
        dstack: [0; 64], tds: 0,
        rstack: [0; 64], trs: 0 };
    init_dictionary(&mut c);
    return c;
}

fn create(c: &mut Core, name: ShortName) {
    let addr: usize = c.here as usize;
    c.ram[addr+0..=addr+1].copy_from_slice(&c.dp.to_le_bytes());
    c.dp = addr as u16;
    c.ram[addr+2] = name.length;
    c.ram[addr+3..=addr+5].copy_from_slice(&name.bytes);
    c.here = (addr+6) as u16;
}

fn find(c: &mut Core, name: ShortName) -> Option<u16> {
    let mut addr = c.dp as usize;
    while addr != 0 {
        if c.ram[addr+2] == name.length {
            if c.ram[addr+3..=addr+5] == name.bytes {
                return Some((addr+6) as u16);
            }
        }
        addr = u16::from_le_bytes(c.ram[addr..=addr+1].try_into().unwrap()) as usize;
    }
    return None;
}

fn init_dictionary(c: &mut Core) {
    let mut opcode = 65535;
    for p in PRIMITIVES {
        create(c, p.name);
        comma(c, opcode);
        opcode -= 1;
    }
}

fn push(c: &mut Core, val: u16) {
    c.dstack[c.tds] = val;
    c.tds += 1;
}

fn pop(c: &mut Core) -> u16 {
    c.tds -= 1;
    return c.dstack[c.tds];
}

fn to_r(c: &mut Core, val: u16) {
    c.rstack[c.trs] = val;
    c.trs += 1;
}

fn from_r(c: &mut Core) -> u16 {
    c.trs -= 1;
    return c.rstack[c.trs];
}

fn fetch(c: &mut Core) -> u16 {
    let ip = c.ip as usize;
    let opcode = u16::from_le_bytes(c.ram[ip..=ip+1].try_into().unwrap());
    c.ip += 2;
    return opcode;
}

fn execute(c: &mut Core, opcode: u16) {
    let primitive_index = (65535 - opcode) as usize;
    if primitive_index < PRIMITIVES.len() {
        (PRIMITIVES[primitive_index].f)(c);
    } else {
        // call
        to_r(c, c.ip);
        c.ip = opcode;
    }
}

fn step(c: &mut Core) {
    let opcode = fetch(c);
    execute(c, opcode);
}

fn inner(c: &mut Core) {
    while c.ip != 2 {
        step(c);
    }
}

fn ret(c: &mut Core) {
    if c.trs == 0 {
        std::process::exit(0);
    }
    c.ip = from_r(c);
}

fn dot(c: &mut Core) {
    print!("{} ", pop(c));
}

fn comma(c: &mut Core, val: u16) {
    let addr = c.here as usize;
    c.ram[addr..=addr+1].copy_from_slice(&val.to_le_bytes());
    c.here += 2;
}

fn store(c: &mut Core) {
    let addr = pop(c) as usize;
    let val = pop(c);
    c.ram[addr..=addr+1].copy_from_slice(&val.to_le_bytes());
}

fn load(c: &mut Core) {
    let addr = pop(c) as usize;
    push(c, u16::from_le_bytes(c.ram[addr..=addr+1].try_into().unwrap()));
}

fn add(c: &mut Core) {
    let v1 = pop(c);
    let v2 = pop(c);
    push(c, v1 + v2);
}

fn sub(c: &mut Core) {
    let v1 = pop(c);
    let v2 = pop(c);
    push(c, v2 - v1);
}

fn mul(c: &mut Core) {
    let v1 = pop(c);
    let v2 = pop(c);
    push(c, v1 * v2);
}

fn div(c: &mut Core) {
    let v1 = pop(c);
    let v2 = pop(c);
    push(c, v2 / v1);
}

fn outer(c: &mut Core, s: &str) {
    let ss = s.trim();
    let tokens = ss.split(" ");
    for t in tokens {
        match t {
            "s" => {
                step(c);
            },
            "g" => {
                c.ip = 0;
                inner(c);
            },
            "dmp" => {
                println!("{:?}", c);
            },
            _ => {
                match find(c, truncate_name(t)) {
                    Some(addr) => {
                        c.ip = addr;
                        inner(c);
                    }
                    None => {
                        let val = t.parse::<u16>();
                        match val {
                            Ok(n) => { push(c, n) }
                            Err(_) => { if t != "" { println!("{}?", t) }}
                        }
                    }
                }
            }
        }
    }
}

fn main() {
    let mut c = new_core();
    loop {
        let mut buf = String::new();
        match io::stdin().read_line(&mut buf) {
            Ok(_) => { outer(&mut c, &buf); println!(" ok");}
            Err(_) => { break; }
        }
    }
    //push(&mut c, 56); push(&mut c, 9); mul(&mut c); dot(&mut c);
    //let v = pop(&mut c); call(&mut c, v);
    //println!("{:?}", c);
}