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#[derive(Debug, Clone, Copy, PartialEq)]
pub enum TokenType {
OneOrMore, // +
AnyNo, // *
Infinite, // ^
Maybe, // ?
Option, // |
Padding, // ;
BracOpen, // (
BracClose, // )
Colon, // :
Character, // '...'
Probability, // <...>
Regex, // [...]
Identifier, // variable names
}
#[derive(Debug, Clone)]
pub struct Token {
pub typ: TokenType,
pub text: String,
}
impl Token {
fn new(_: usize, typ: TokenType, text: String) -> Self {
Token { typ, text }
}
}
#[derive(Debug, Clone)]
pub struct ScanError {
_msg: String,
}
impl ScanError {
fn new(msg: String) -> Self {
ScanError { _msg: msg }
}
}
pub struct Scanner {
pos: usize, // current byte offset
width: usize, // width of last char in bytes
curr_r: char, // current rune/char
tokens: Vec<Token>,
chars: Vec<char>, // cached char array for easier iteration
}
impl Scanner {
pub fn new(input: String) -> Self {
let chars: Vec<char> = input.chars().collect();
Scanner {
pos: 0,
width: 0,
curr_r: '\0',
tokens: Vec::new(),
chars,
}
}
// advance and return the next char
fn next(&mut self) -> Option<char> {
if self.pos >= self.chars.len() {
self.width = 0;
self.curr_r = '\0';
return None;
}
let c = self.chars[self.pos];
self.width = 1;
self.pos += 1;
self.curr_r = c;
Some(c)
}
// look at the next char without consuming it
fn peek(&mut self) -> Option<char> {
if self.pos >= self.chars.len() {
return None;
}
Some(self.chars[self.pos])
}
fn scan_delimited(
&mut self,
open: char,
close: char,
_allow_escapes: bool,
) -> Result<String, ScanError> {
let mut buf = String::new();
loop {
match self.next() {
None => {
return Err(ScanError::new(format!("unterminated '{}'", open)));
}
Some(r) => {
if r == close {
return Ok(buf);
}
buf.push(r);
}
}
}
}
fn scan_identifier(&mut self) -> String {
let mut buf = String::new();
buf.push(self.curr_r);
// Keep reading while next chars are valid identifier parts
loop {
match self.peek() {
Some(r) if is_ident_part(r) => {
self.next();
buf.push(self.curr_r);
}
_ => break,
}
}
buf
}
pub fn scan(mut self) -> (Vec<Token>, Vec<ScanError>) {
let mut errs = Vec::new();
while let Some(c) = self.next() {
match c {
'+' => {
self.tokens.push(Token::new(
self.pos - 1,
TokenType::OneOrMore,
String::new(),
));
}
'*' => {
self.tokens
.push(Token::new(self.pos - 1, TokenType::AnyNo, String::new()));
}
'^' => {
self.tokens
.push(Token::new(self.pos - 1, TokenType::Infinite, String::new()));
}
'?' => {
self.tokens
.push(Token::new(self.pos - 1, TokenType::Maybe, String::new()));
}
'|' => {
self.tokens
.push(Token::new(self.pos - 1, TokenType::Option, String::new()));
}
';' => {
self.tokens
.push(Token::new(self.pos - 1, TokenType::Padding, String::new()));
}
'(' => {
self.tokens
.push(Token::new(self.pos - 1, TokenType::BracOpen, String::new()));
}
')' => {
self.tokens.push(Token::new(
self.pos - 1,
TokenType::BracClose,
String::new(),
));
}
':' => {
self.tokens
.push(Token::new(self.pos - 1, TokenType::Colon, String::new()));
}
'\'' => match self.scan_delimited('\'', '\'', false) {
Ok(val) => {
self.tokens.push(Token::new(
self.pos - val.len() - 2,
TokenType::Character,
val,
));
}
Err(err) => {
errs.push(err);
}
},
'<' => match self.scan_delimited('<', '>', false) {
Ok(val) => {
self.tokens.push(Token::new(
self.pos - val.len() - 2,
TokenType::Probability,
val,
));
}
Err(err) => {
errs.push(err);
}
},
'[' => match self.scan_delimited('[', ']', false) {
Ok(val) => {
self.tokens.push(Token::new(
self.pos - val.len() - 2,
TokenType::Regex,
val,
));
}
Err(err) => {
errs.push(err);
}
},
_ => {
if is_ident_start(c) {
let buff = self.scan_identifier();
if !buff.is_empty() {
self.tokens.push(Token::new(
self.pos - buff.len(),
TokenType::Identifier,
buff,
));
}
}
// Ignore whitespace and other characters
}
}
}
(self.tokens, errs)
}
}
// Helper functions
fn is_alpha(r: char) -> bool {
r.is_ascii_alphabetic()
}
fn is_digit(r: char) -> bool {
r.is_ascii_digit()
}
fn is_ident_start(r: char) -> bool {
is_alpha(r) || r == '_'
}
fn is_ident_part(r: char) -> bool {
is_alpha(r) || is_digit(r) || r == '_'
}