-
Notifications
You must be signed in to change notification settings - Fork 7
Commit
This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
This implements the [parsing](http://www.craftinginterpreters.com/parsing-expressions.htmll). A few differences: * `matches!` is a macro to allow varargs. It stands in for `match` from the Java version. * The literals are typed via `LiteralValue`. * `primary` does not use `matches!` but the Rust pattern matching to extract values. * We use `Result` instead of exceptions.
- Loading branch information
Showing
6 changed files
with
304 additions
and
13 deletions.
There are no files selected for viewing
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,237 @@ | ||
| use crate::error::{parser_error, Error}; | ||
| use crate::syntax::{Expr, LiteralValue}; | ||
| use crate::token::{Token, TokenType}; | ||
|
|
||
| pub struct Parser<'t> { | ||
| tokens: &'t Vec<Token>, | ||
| current: usize, | ||
| } | ||
|
|
||
| /// AKA match in Chapter 6. | ||
| macro_rules! matches { | ||
| ( $sel:ident, $( $x:expr ),* ) => { | ||
| { | ||
| if $( $sel.check($x) )||* { | ||
| $sel.advance(); | ||
| true | ||
| } else { | ||
| false | ||
| } | ||
| } | ||
| }; | ||
| } | ||
|
|
||
| impl<'t> Parser<'t> { | ||
| pub fn new(tokens: &'t Vec<Token>) -> Self { | ||
| Parser { tokens, current: 0 } | ||
| } | ||
|
|
||
| pub fn parse(&mut self) -> Option<Expr> { | ||
| self.expression().ok() | ||
| } | ||
|
|
||
| fn expression(&mut self) -> Result<Expr, Error> { | ||
| self.equality() | ||
| } | ||
|
|
||
| fn equality(&mut self) -> Result<Expr, Error> { | ||
| let mut expr = self.comparison()?; | ||
|
|
||
| while matches!(self, TokenType::BangEqual, TokenType::EqualEqual) { | ||
| let operator: Token = (*self.previous()).clone(); | ||
| let right: Expr = self.comparison()?; | ||
| expr = Expr::Binary { | ||
| left: Box::new(expr), | ||
| operator, | ||
| right: Box::new(right), | ||
| }; | ||
| } | ||
|
|
||
| Ok(expr) | ||
| } | ||
|
|
||
| fn check(&self, token_type: TokenType) -> bool { | ||
| if self.is_at_end() { | ||
| return false; | ||
| } | ||
|
|
||
| token_type == self.peek().tpe | ||
| } | ||
|
|
||
| fn consume(&mut self, tpe: TokenType, message: &str) -> Result<Token, Error> { | ||
| if self.check(tpe) { | ||
| Ok(self.advance().clone()) | ||
| } else { | ||
| Err(self.error(self.peek(), message)) | ||
| } | ||
| } | ||
|
|
||
| fn advance(&mut self) -> &Token { | ||
| if !self.is_at_end() { | ||
| self.current += 1; | ||
| } | ||
| self.previous() | ||
| } | ||
|
|
||
| fn previous(&self) -> &Token { | ||
| self.tokens | ||
| .get(self.current - 1) | ||
| .expect("Previous was empty.") | ||
| } | ||
|
|
||
| fn error(&self, token: &Token, message: &str) -> Error { | ||
| parser_error(token, message); | ||
| Error::Parse | ||
| } | ||
|
|
||
| fn synchronize(&mut self) { | ||
| self.advance(); | ||
|
|
||
| while !self.is_at_end() { | ||
| if self.previous().tpe == TokenType::Semicolon { | ||
| return; | ||
| } | ||
|
|
||
| match self.peek().tpe { | ||
| TokenType::Class | ||
| | TokenType::Fun | ||
| | TokenType::Var | ||
| | TokenType::For | ||
| | TokenType::If | ||
| | TokenType::While | ||
| | TokenType::Print | ||
| | TokenType::Return => return, | ||
| _ => self.advance(), | ||
| }; | ||
| } | ||
| } | ||
|
|
||
| fn peek(&self) -> &Token { | ||
| self.tokens | ||
| .get(self.current) | ||
| .expect("Peek into end of token stream.") | ||
| } | ||
|
|
||
| fn is_at_end(&self) -> bool { | ||
| self.peek().tpe == TokenType::EOF | ||
| } | ||
|
|
||
| fn comparison(&mut self) -> Result<Expr, Error> { | ||
| let mut expr = self.addition()?; | ||
|
|
||
| while matches!( | ||
| self, | ||
| TokenType::Greater, | ||
| TokenType::GreaterEqual, | ||
| TokenType::Less, | ||
| TokenType::LessEqual | ||
| ) { | ||
| let operator: Token = self.previous().clone(); | ||
| let right = self.addition()?; | ||
| expr = Expr::Binary { | ||
| left: Box::new(expr), | ||
| operator, | ||
| right: Box::new(right), | ||
| } | ||
| } | ||
|
|
||
| Ok(expr) | ||
| } | ||
|
|
||
| fn addition(&mut self) -> Result<Expr, Error> { | ||
| let mut expr = self.multiplication()?; | ||
|
|
||
| while matches!(self, TokenType::Minus, TokenType::Plus) { | ||
| let operator: Token = self.previous().clone(); | ||
| let right = self.multiplication()?; | ||
| expr = Expr::Binary { | ||
| left: Box::new(expr), | ||
| operator, | ||
| right: Box::new(right), | ||
| } | ||
| } | ||
|
|
||
| Ok(expr) | ||
| } | ||
|
|
||
| fn multiplication(&mut self) -> Result<Expr, Error> { | ||
| let mut expr = self.unary()?; | ||
|
|
||
| while matches!(self, TokenType::Slash, TokenType::Star) { | ||
| let operator: Token = self.previous().clone(); | ||
| let right = self.unary()?; | ||
| expr = Expr::Binary { | ||
| left: Box::new(expr), | ||
| operator, | ||
| right: Box::new(right), | ||
| } | ||
| } | ||
|
|
||
| Ok(expr) | ||
| } | ||
|
|
||
| fn unary(&mut self) -> Result<Expr, Error> { | ||
| if matches!(self, TokenType::Bang, TokenType::Minus) { | ||
| let operator: Token = self.previous().clone(); | ||
| let right = self.unary()?; | ||
| Ok(Expr::Unary { | ||
| operator, | ||
| right: Box::new(right), | ||
| }) | ||
| } else { | ||
| self.primary() | ||
| } | ||
| } | ||
|
|
||
| fn primary(&mut self) -> Result<Expr, Error> { | ||
| // We don't use matches!() here since we want to extract the literals. | ||
| let expr = match &self.peek().tpe { | ||
| TokenType::False => Expr::Literal { | ||
| value: LiteralValue::Boolean(false), | ||
| }, | ||
| TokenType::True => Expr::Literal { | ||
| value: LiteralValue::Boolean(true), | ||
| }, | ||
| TokenType::Nil => Expr::Literal { | ||
| value: LiteralValue::Null, | ||
| }, | ||
| TokenType::String { literal } => Expr::Literal { | ||
| value: LiteralValue::String(literal.clone()), | ||
| }, | ||
| TokenType::Number { literal } => Expr::Literal { | ||
| value: LiteralValue::Number(literal.clone()), | ||
| }, | ||
| TokenType::LeftParen => { | ||
| let expr = self.expression()?; | ||
| self.consume(TokenType::RightParen, "Expected ')' after expression.")?; | ||
| Expr::Grouping { | ||
| expression: Box::new(expr), | ||
| } | ||
| } | ||
| _ => return Err(self.error(self.peek(), "Expect expression.")), | ||
| }; | ||
|
|
||
| self.advance(); | ||
|
|
||
| Ok(expr) | ||
| } | ||
| } | ||
|
|
||
| #[cfg(test)] | ||
| mod tests { | ||
| use super::*; | ||
| use crate::scanner::Scanner; | ||
| use crate::syntax::AstPrinter; | ||
|
|
||
| #[test] | ||
| fn test_parser() { | ||
| let mut scanner = Scanner::new("-123 * 45.67".to_string()); | ||
| let tokens = scanner.scan_tokens(); | ||
|
|
||
| let mut parser = Parser::new(tokens); | ||
| let expression = parser.parse().expect("Could not parse sample code."); | ||
| let printer = AstPrinter; | ||
|
|
||
| assert_eq!(printer.print(expression), "(* (- 123) 45.67)"); | ||
| } | ||
| } |
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Oops, something went wrong.