use regex::Regex; use std::rc::Rc; use crate::{ lexer::Token, token::{Expr::{self, Null, List, Vector}, Return, Error::{self, ErrorString}}, list, vector, }; const INT_REGEX: &str = r#"^-?[0-9]+$"#; const STRING_REGEX: &str = r#""(?:\\.|[^\\"])*""#; struct Reader { tokens: Vec, position: usize, } impl Reader { fn new(tokens: Vec) -> Reader { Reader { tokens, position: 0, } } fn next(&mut self) -> Result<&Token, Error> { self.position += 1; Ok(self.tokens.get(self.position - 1).ok_or(ErrorString("Underflow".to_string()))?) } fn peek(&mut self) -> Result<&Token, Error> { Ok(self.tokens.get(self.position).ok_or(ErrorString("Underflow".to_string()))?) } } fn read_atom(reader: &mut Reader) -> Return { let int_regex = Regex::new(INT_REGEX).unwrap(); let string_regex = Regex::new(STRING_REGEX).unwrap(); let token = reader.next()?; match &token.value[..] { "null" => Ok(Expr::Null), "true" => Ok(Expr::Bool(true)), "false" => Ok(Expr::Bool(false)), _ => { if int_regex.is_match(&token.value) { Ok(Expr::Number(token.value.parse().unwrap())) } else if string_regex.is_match(&token.value) { Ok(Expr::String(token.value[1..token.value.len() - 1].to_string())) } else { Ok(Expr::Symbol(token.value.to_string())) } } } } fn read_sequence(reader: &mut Reader, end: &str) -> Return { let mut sequence: Vec = Vec::new(); reader.next()?; loop { let token = match reader.peek() { Ok(token) => token, Err(_) => return Err(ErrorString(format!("Unexpected end of input, found '{}'", end))), }; if token.value == end { break; } sequence.push(read_form(reader)?) } let _ = reader.next(); match end { ")" => Ok(list!(sequence)), "]" => Ok(vector!(sequence)), _ => return Err(ErrorString(format!("Unknown sequence end value: '{}'", end))), } } fn read_form(reader: &mut Reader) -> Return { let token = reader.peek()?; match &token.value[..] { "(" => read_sequence(reader, ")"), ")" => Err(ErrorString("Unexpected ')'".to_string())), "[" => read_sequence(reader, "]"), "]" => Err(ErrorString("Unexpected ']'".to_string())), _ => read_atom(reader), } } pub fn parse(tokens: Vec) -> Return { if tokens.len() == 0 { return Ok(Null); } read_form(&mut Reader::new(tokens)) }