use std::io; use std::io::Write; use std::io::BufRead; use std::char; use std::slice::Iter; use Token::*; fn main() { println!("Unnamed language 0.01"); repl(); } #[derive(Debug, Clone)] enum Token { EOF, Separator, LParen, RParen, Comma, NumLiteral(f64), StrLiteral(String), Identifier(String) /* Keyword(Keyword) */ //implement in future } #[derive(Debug)] enum ASTNode { Name(String), Number(f64), BinOp(Box, Box, Box), Binding(String, Box) } enum ParseResult { Ok(ASTNode), Err(String) } fn repl() { let stdin = io::stdin(); let mut stdout = io::stdout(); let mut buf = String::with_capacity(20); loop { print!(">> "); stdout.flush().ok(); let line = stdin.lock().read_line(&mut buf); match line { Ok(_) => { if buf.is_empty() { break; } let tokens = tokenize(&buf); buf.clear(); println!("Tokens: {:?}", tokens); match parse(tokens) { ParseResult::Ok(ast) => println!("AST: {:?}", ast), ParseResult::Err(err) => println!("Error: {}", err) } /* let eval = evaluate(&ast); println!("{}", eval); */ }, Err(err) => { println!("Error: {}", err); } } } } fn tokenize(input: &str) -> Vec { let mut tokens = Vec::new(); let mut iterator = input.chars().peekable(); fn ends_identifier(c: char) -> bool { match c { c if char::is_whitespace(c) => true, ',' => true, ';' => true, '(' => true, ')' => true, _ => false } } while let Some(c) = iterator.next() { if char::is_whitespace(c) { continue; } else if c == '"' { let mut buffer = String::with_capacity(20); while let Some(x) = iterator.next() { if x == '"' { break; } buffer.push(x); } tokens.push(Token::StrLiteral(buffer)); } else if c == '#' { while let Some(x) = iterator.next() { if x == '\n' { break; } } } else if c == ';' || c == '\n' { tokens.push(Token::Separator); } else if c == '(' { tokens.push(Token::LParen); } else if c == ')' { tokens.push(Token::RParen); } else if c == ',' { tokens.push(Token::Comma); } else { let mut buffer = String::with_capacity(20); buffer.push(c); while let Some(x) = iterator.peek().cloned() { if ends_identifier(x) { break; } buffer.push(iterator.next().unwrap()); } match buffer.parse::() { Ok(f) => tokens.push(Token::NumLiteral(f)), _ => tokens.push(Token::Identifier(buffer)) } } } tokens.push(Token::EOF); tokens } fn parse(input: Vec) -> ParseResult { let mut tokens = input.iter(); if let ParseResult::Ok(ast) = let_expression(&mut tokens) { if expect(EOF, &mut tokens) { return ParseResult::Ok(ast); } } return ParseResult::Err("Bad parse".to_string()); } fn expect(tok: Token, tokens: &mut Iter) -> bool { if let Some(n) = tokens.next() { let next = (*n).clone(); return match (tok, next) { (EOF, EOF) => true, (Separator, Separator) => true, (LParen, LParen) => true, (RParen, RParen) => true, (Comma, Comma) => true, (NumLiteral(_), NumLiteral(_)) => true, (StrLiteral(_), StrLiteral(_)) => true, (Identifier(ref i1), Identifier(ref i2)) => i1 == i2, _ => false } } return false; } fn let_expression<'a>(input: &mut Iter) -> ParseResult { if expect(Identifier("let".to_string()), input) { if let Some(&Identifier(ref name)) = input.next() { if let Some(&Identifier(ref s)) = input.next() { if s == "=" { let next = input.next(); if let Some(&Identifier(ref value)) = next { let ast = ASTNode::Binding(name.clone(), Box::new(ASTNode::Name(value.clone()))); return ParseResult::Ok(ast); } if let Some(&StrLiteral(ref value)) = next { let ast = ASTNode::Binding(name.clone(), Box::new(ASTNode::Name(value.clone()))); return ParseResult::Ok(ast); } if let Some(&NumLiteral(n)) = next { let ast = ASTNode::Binding(name.clone(), Box::new(ASTNode::Number(n))); return ParseResult::Ok(ast); } } } } } return ParseResult::Err("Bad parse".to_string()); }