tseeker-pub/rust-crafting-interpreters-part-1
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Parser - Refactored error handling

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This commit is contained in:
Emmanuel BENOîT 2023-01-03 23:07:49 +01:00
parent acb29e7123
commit 0443754007
1 changed files with 63 additions and 74 deletions
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137
src/parser.rs
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@ -2,7 +2,7 @@ use std::collections::HashSet;
use crate::{ use crate::{
ast, ast,
errors::{ErrorHandler, ParserError}, errors::{ErrorHandler, ErrorKind, SloxError, SloxResult},
tokens::{Token, TokenType}, tokens::{Token, TokenType},
}; };
@ -62,9 +62,6 @@ impl FunctionKind {
} }
} }
/// The result of one of the parser's functions.
type ParserResult<T> = Result<T, ParserError>;
impl Parser { impl Parser {
/// Initialize the parser. /// Initialize the parser.
pub fn new(tokens: Vec<Token>) -> Self { pub fn new(tokens: Vec<Token>) -> Self {
@ -120,7 +117,7 @@ impl Parser {
match self.parse_statement() { match self.parse_statement() {
Ok(node) => stmts.push(node), Ok(node) => stmts.push(node),
Err(err) => { Err(err) => {
err.report(err_hdl); err_hdl.report(err);
self.synchronize() self.synchronize()
} }
} }
@ -146,7 +143,7 @@ impl Parser {
/// statement := loop_control_statement /// statement := loop_control_statement
/// statement := return_statement /// statement := return_statement
/// ``` /// ```
fn parse_statement(&mut self) -> ParserResult<ast::StmtNode> { fn parse_statement(&mut self) -> SloxResult<ast::StmtNode> {
if self.expect(&[TokenType::Var]).is_some() { if self.expect(&[TokenType::Var]).is_some() {
self.parse_var_declaration() self.parse_var_declaration()
} else if self.expect(&[TokenType::Fun]).is_some() { } else if self.expect(&[TokenType::Fun]).is_some() {
@ -184,7 +181,7 @@ impl Parser {
/// ``` /// ```
/// expression_stmt := expression ";" /// expression_stmt := expression ";"
/// ``` /// ```
fn parse_expression_stmt(&mut self) -> ParserResult<ast::StmtNode> { fn parse_expression_stmt(&mut self) -> SloxResult<ast::StmtNode> {
let expression = self.parse_expression()?; let expression = self.parse_expression()?;
self.consume(&TokenType::Semicolon, "expected ';' after expression")?; self.consume(&TokenType::Semicolon, "expected ';' after expression")?;
Ok(ast::StmtNode::Expression(expression)) Ok(ast::StmtNode::Expression(expression))
@ -195,10 +192,10 @@ impl Parser {
/// var_declaration := "var" IDENTIFIER ";" /// var_declaration := "var" IDENTIFIER ";"
/// var_declaration := "var" IDENTIFIER "=" expression ";" /// var_declaration := "var" IDENTIFIER "=" expression ";"
/// ``` /// ```
fn parse_var_declaration(&mut self) -> ParserResult<ast::StmtNode> { fn parse_var_declaration(&mut self) -> SloxResult<ast::StmtNode> {
let name = match self.peek().token_type { let name = match self.peek().token_type {
TokenType::Identifier(_) => self.advance().clone(), TokenType::Identifier(_) => self.advance().clone(),
_ => return Err(ParserError::new(self.peek(), "expected variable name")), _ => return self.error("expected variable name"),
}; };
let initializer: Option<ast::ExprNode> = match self.expect(&[TokenType::Equal]) { let initializer: Option<ast::ExprNode> = match self.expect(&[TokenType::Equal]) {
Some(_) => Some(self.parse_expression()?), Some(_) => Some(self.parse_expression()?),
@ -217,16 +214,11 @@ impl Parser {
/// function := IDENTIFIER function_info /// function := IDENTIFIER function_info
/// ``` /// ```
/// The `kind` parameter is used to generate error messages. /// The `kind` parameter is used to generate error messages.
fn parse_fun_declaration(&mut self, kind: FunctionKind) -> ParserResult<ast::StmtNode> { fn parse_fun_declaration(&mut self, kind: FunctionKind) -> SloxResult<ast::StmtNode> {
// Read the name // Read the name
let name = match self.peek().token_type { let name = match self.peek().token_type {
TokenType::Identifier(_) => self.advance().clone(), TokenType::Identifier(_) => self.advance().clone(),
_ => { _ => return self.error_mv(format!("expected {} name", kind.name())),
return Err(ParserError::new(
self.peek(),
&format!("expected {} name", kind.name()),
))
}
}; };
let (params, block) = self.parse_function_info(kind)?; let (params, block) = self.parse_function_info(kind)?;
Ok(ast::StmtNode::FunDecl { Ok(ast::StmtNode::FunDecl {
@ -244,7 +236,7 @@ impl Parser {
fn parse_function_info( fn parse_function_info(
&mut self, &mut self,
kind: FunctionKind, kind: FunctionKind,
) -> ParserResult<(Vec<Token>, Vec<ast::StmtNode>)> { ) -> SloxResult<(Vec<Token>, Vec<ast::StmtNode>)> {
// Read the list of parameter names // Read the list of parameter names
self.consume( self.consume(
&TokenType::LeftParen, &TokenType::LeftParen,
@ -256,26 +248,20 @@ impl Parser {
let mut names: HashSet<String> = HashSet::new(); let mut names: HashSet<String> = HashSet::new();
loop { loop {
if params.len() >= kind.max_params() { if params.len() >= kind.max_params() {
return Err(ParserError::new( return self.error_mv(format!(
self.peek(), "{} can't have more than {} parameters",
&format!( kind.name(),
"{} can't have more than {} parameters", kind.max_params()
kind.name(),
kind.max_params()
),
)); ));
} }
if let TokenType::Identifier(name) = &self.peek().token_type { if let TokenType::Identifier(name) = &self.peek().token_type {
if names.contains(name) { if names.contains(name) {
return Err(ParserError::new( return self.error_mv(format!("duplicate {} parameter", kind.name()));
self.peek(),
&format!("duplicate {} parameter", kind.name()),
));
} }
names.insert(name.to_owned()); names.insert(name.to_owned());
params.push(self.advance().clone()); params.push(self.advance().clone());
} else { } else {
return Err(ParserError::new(self.peek(), "parameter name expected")); return self.error("parameter name expected");
} }
if self.expect(&[TokenType::Comma]).is_none() { if self.expect(&[TokenType::Comma]).is_none() {
break; break;
@ -302,7 +288,7 @@ impl Parser {
/// ``` /// ```
/// block := "{" statement* "}" /// block := "{" statement* "}"
/// ``` /// ```
fn parse_block(&mut self) -> ParserResult<ast::StmtNode> { fn parse_block(&mut self) -> SloxResult<ast::StmtNode> {
let mut stmts: Vec<ast::StmtNode> = Vec::new(); let mut stmts: Vec<ast::StmtNode> = Vec::new();
while !(self.check(&TokenType::RightBrace) || self.is_at_end()) { while !(self.check(&TokenType::RightBrace) || self.is_at_end()) {
stmts.push(self.parse_statement()?); stmts.push(self.parse_statement()?);
@ -316,7 +302,7 @@ impl Parser {
/// if_statement := "if" "(" expression ")" statement /// if_statement := "if" "(" expression ")" statement
/// if_statement := "if" "(" expression ")" statement "else" statement /// if_statement := "if" "(" expression ")" statement "else" statement
/// ``` /// ```
fn parse_if_statement(&mut self) -> ParserResult<ast::StmtNode> { fn parse_if_statement(&mut self) -> SloxResult<ast::StmtNode> {
self.consume(&TokenType::LeftParen, "expected '(' after 'if'")?; self.consume(&TokenType::LeftParen, "expected '(' after 'if'")?;
let expression = self.parse_expression()?; let expression = self.parse_expression()?;
self.consume( self.consume(
@ -340,15 +326,10 @@ impl Parser {
/// labelled_loop := "@" IDENTIFIER while_statement /// labelled_loop := "@" IDENTIFIER while_statement
/// labelled_loop := "@" IDENTIFIER for_statement /// labelled_loop := "@" IDENTIFIER for_statement
/// ``` /// ```
fn parse_labelled_loop(&mut self) -> ParserResult<ast::StmtNode> { fn parse_labelled_loop(&mut self) -> SloxResult<ast::StmtNode> {
let name_token = match self.peek().token_type { let name_token = match self.peek().token_type {
TokenType::Identifier(_) => self.advance().clone(), TokenType::Identifier(_) => self.advance().clone(),
_ => { _ => return self.error("identifier expected after '@'"),
return Err(ParserError::new(
self.peek(),
"identifier expected after '@'",
))
}
}; };
if self.expect(&[TokenType::While]).is_some() { if self.expect(&[TokenType::While]).is_some() {
@ -356,10 +337,7 @@ impl Parser {
} else if self.expect(&[TokenType::For]).is_some() { } else if self.expect(&[TokenType::For]).is_some() {
self.parse_for_statement(Some(name_token)) self.parse_for_statement(Some(name_token))
} else { } else {
Err(ParserError::new( self.error("'while' or 'for' expected after loop label")
self.peek(),
"'while' or 'for' expected after loop label",
))
} }
} }
@ -367,7 +345,7 @@ impl Parser {
/// ``` /// ```
/// while_statement := "while" "(" expression ")" statement /// while_statement := "while" "(" expression ")" statement
/// ``` /// ```
fn parse_while_statement(&mut self, label: Option<Token>) -> ParserResult<ast::StmtNode> { fn parse_while_statement(&mut self, label: Option<Token>) -> SloxResult<ast::StmtNode> {
self.consume(&TokenType::LeftParen, "expected '(' after 'while'")?; self.consume(&TokenType::LeftParen, "expected '(' after 'while'")?;
let condition = self.parse_expression()?; let condition = self.parse_expression()?;
self.consume( self.consume(
@ -395,7 +373,7 @@ impl Parser {
/// for_initializer := expression /// for_initializer := expression
/// for_initializer := /// for_initializer :=
/// ``` /// ```
fn parse_for_statement(&mut self, label: Option<Token>) -> ParserResult<ast::StmtNode> { fn parse_for_statement(&mut self, label: Option<Token>) -> SloxResult<ast::StmtNode> {
self.consume(&TokenType::LeftParen, "expected '(' after 'for'")?; self.consume(&TokenType::LeftParen, "expected '(' after 'for'")?;
let initializer = if self.expect(&[TokenType::Semicolon]).is_some() { let initializer = if self.expect(&[TokenType::Semicolon]).is_some() {
@ -458,11 +436,12 @@ impl Parser {
/// loop_control_statement := "break" ( IDENTIFIER )? ";" /// loop_control_statement := "break" ( IDENTIFIER )? ";"
/// loop_control_statement := "continue" ( IDENTIFIER )? ";" /// loop_control_statement := "continue" ( IDENTIFIER )? ";"
/// ``` /// ```
fn parse_loop_control_statement(&mut self, stmt_token: &Token) -> ParserResult<ast::StmtNode> { fn parse_loop_control_statement(&mut self, stmt_token: &Token) -> SloxResult<ast::StmtNode> {
if self.loop_state() == &LoopParsingState::None { if self.loop_state() == &LoopParsingState::None {
return Err(ParserError::new( return Err(SloxError::with_token(
ErrorKind::Parse,
stmt_token, stmt_token,
&format!( format!(
"'{}' statement found outside of loop body", "'{}' statement found outside of loop body",
stmt_token.lexeme stmt_token.lexeme
), ),
@ -473,9 +452,10 @@ impl Parser {
let name_token = self.advance().clone(); let name_token = self.advance().clone();
if !self.find_named_loop(&name_token.lexeme) { if !self.find_named_loop(&name_token.lexeme) {
self.expect(&[TokenType::Semicolon]); self.expect(&[TokenType::Semicolon]);
return Err(ParserError::new( return Err(SloxError::with_token(
ErrorKind::Parse,
&name_token, &name_token,
&format!("no reachable loop named '{}'", name_token.lexeme), format!("no reachable loop named '{}'", name_token.lexeme),
)); ));
} }
Some(name_token) Some(name_token)
@ -497,7 +477,7 @@ impl Parser {
/// ``` /// ```
/// return_statement := "return" expression? ";" /// return_statement := "return" expression? ";"
/// ``` /// ```
fn parse_return_statement(&mut self, ret_token: &Token) -> ParserResult<ast::StmtNode> { fn parse_return_statement(&mut self, ret_token: &Token) -> SloxResult<ast::StmtNode> {
if self.can_use_return() { if self.can_use_return() {
let value = if self.check(&TokenType::Semicolon) { let value = if self.check(&TokenType::Semicolon) {
None None
@ -510,9 +490,10 @@ impl Parser {
value, value,
}) })
} else { } else {
Err(ParserError::new( Err(SloxError::with_token(
ErrorKind::Parse,
ret_token, ret_token,
"'return' found outside of function", "'return' found outside of function".to_owned(),
)) ))
} }
} }
@ -521,7 +502,7 @@ impl Parser {
/// ``` /// ```
/// expression := assignment /// expression := assignment
/// ``` /// ```
fn parse_expression(&mut self) -> ParserResult<ast::ExprNode> { fn parse_expression(&mut self) -> SloxResult<ast::ExprNode> {
self.parse_assignment() self.parse_assignment()
} }
@ -530,7 +511,7 @@ impl Parser {
/// assignment := IDENTIFIER "=" equality /// assignment := IDENTIFIER "=" equality
/// assignment := equality /// assignment := equality
/// ``` /// ```
fn parse_assignment(&mut self) -> ParserResult<ast::ExprNode> { fn parse_assignment(&mut self) -> SloxResult<ast::ExprNode> {
let expr = self.parse_logic_or()?; let expr = self.parse_logic_or()?;
if let Some(equals) = self.expect(&[TokenType::Equal]) { if let Some(equals) = self.expect(&[TokenType::Equal]) {
let value = self.parse_assignment()?; let value = self.parse_assignment()?;
@ -540,7 +521,7 @@ impl Parser {
value: Box::new(value), value: Box::new(value),
}) })
} else { } else {
Err(ParserError::new(&equals, "invalid assignment target")) self.error("invalid assignment target")
} }
} else { } else {
Ok(expr) Ok(expr)
@ -551,7 +532,7 @@ impl Parser {
/// ``` /// ```
/// logic_or := logic_and ( "or" logic_and )* /// logic_or := logic_and ( "or" logic_and )*
/// ``` /// ```
fn parse_logic_or(&mut self) -> ParserResult<ast::ExprNode> { fn parse_logic_or(&mut self) -> SloxResult<ast::ExprNode> {
let mut expr = self.parse_logic_and()?; let mut expr = self.parse_logic_and()?;
while let Some(operator) = self.expect(&[TokenType::Or]) { while let Some(operator) = self.expect(&[TokenType::Or]) {
let right = self.parse_logic_and()?; let right = self.parse_logic_and()?;
@ -568,7 +549,7 @@ impl Parser {
/// ``` /// ```
/// logic_and := equality ( "and" equality )* /// logic_and := equality ( "and" equality )*
/// ``` /// ```
fn parse_logic_and(&mut self) -> ParserResult<ast::ExprNode> { fn parse_logic_and(&mut self) -> SloxResult<ast::ExprNode> {
let mut expr = self.parse_equality()?; let mut expr = self.parse_equality()?;
while let Some(operator) = self.expect(&[TokenType::And]) { while let Some(operator) = self.expect(&[TokenType::And]) {
let right = self.parse_equality()?; let right = self.parse_equality()?;
@ -586,7 +567,7 @@ impl Parser {
/// equality := comparison "==" comparison /// equality := comparison "==" comparison
/// equality := comparison "!=" comparison /// equality := comparison "!=" comparison
/// ``` /// ```
fn parse_equality(&mut self) -> ParserResult<ast::ExprNode> { fn parse_equality(&mut self) -> SloxResult<ast::ExprNode> {
let mut expr = self.parse_comparison()?; let mut expr = self.parse_comparison()?;
while let Some(operator) = self.expect(&[TokenType::BangEqual, TokenType::EqualEqual]) { while let Some(operator) = self.expect(&[TokenType::BangEqual, TokenType::EqualEqual]) {
let right = self.parse_comparison()?; let right = self.parse_comparison()?;
@ -604,7 +585,7 @@ impl Parser {
/// comparison := term comparison_operator term /// comparison := term comparison_operator term
/// comparison_operator := "<" | "<=" | ">" | ">=" /// comparison_operator := "<" | "<=" | ">" | ">="
/// ``` /// ```
fn parse_comparison(&mut self) -> ParserResult<ast::ExprNode> { fn parse_comparison(&mut self) -> SloxResult<ast::ExprNode> {
let mut expr = self.parse_term()?; let mut expr = self.parse_term()?;
while let Some(operator) = self.expect(&[ while let Some(operator) = self.expect(&[
TokenType::Greater, TokenType::Greater,
@ -627,7 +608,7 @@ impl Parser {
/// term := factor ( "+" factor )* /// term := factor ( "+" factor )*
/// term := factor ( "-" factor )* /// term := factor ( "-" factor )*
/// ``` /// ```
fn parse_term(&mut self) -> ParserResult<ast::ExprNode> { fn parse_term(&mut self) -> SloxResult<ast::ExprNode> {
let mut expr = self.parse_factor()?; let mut expr = self.parse_factor()?;
while let Some(operator) = self.expect(&[TokenType::Minus, TokenType::Plus]) { while let Some(operator) = self.expect(&[TokenType::Minus, TokenType::Plus]) {
let right = self.parse_factor()?; let right = self.parse_factor()?;
@ -645,7 +626,7 @@ impl Parser {
/// factor := unary ( "*" unary )* /// factor := unary ( "*" unary )*
/// factor := unary ( "/" unary )* /// factor := unary ( "/" unary )*
/// ``` /// ```
fn parse_factor(&mut self) -> ParserResult<ast::ExprNode> { fn parse_factor(&mut self) -> SloxResult<ast::ExprNode> {
let mut expr = self.parse_unary()?; let mut expr = self.parse_unary()?;
while let Some(operator) = self.expect(&[TokenType::Slash, TokenType::Star]) { while let Some(operator) = self.expect(&[TokenType::Slash, TokenType::Star]) {
let right = self.parse_unary()?; let right = self.parse_unary()?;
@ -664,7 +645,7 @@ impl Parser {
/// unary := "!" unary /// unary := "!" unary
/// unary := primary call_arguments* /// unary := primary call_arguments*
/// ``` /// ```
fn parse_unary(&mut self) -> ParserResult<ast::ExprNode> { fn parse_unary(&mut self) -> SloxResult<ast::ExprNode> {
if let Some(operator) = self.expect(&[TokenType::Bang, TokenType::Minus]) { if let Some(operator) = self.expect(&[TokenType::Bang, TokenType::Minus]) {
Ok(ast::ExprNode::Unary { Ok(ast::ExprNode::Unary {
operator, operator,
@ -686,7 +667,7 @@ impl Parser {
/// primary := IDENTIFIER /// primary := IDENTIFIER
/// primary := "fun" function_info /// primary := "fun" function_info
/// ``` /// ```
fn parse_primary(&mut self) -> ParserResult<ast::ExprNode> { fn parse_primary(&mut self) -> SloxResult<ast::ExprNode> {
if self.expect(&[TokenType::LeftParen]).is_some() { if self.expect(&[TokenType::LeftParen]).is_some() {
let expr = self.parse_expression()?; let expr = self.parse_expression()?;
self.consume(&TokenType::RightParen, "expected ')' after expression")?; self.consume(&TokenType::RightParen, "expected ')' after expression")?;
@ -708,7 +689,7 @@ impl Parser {
TokenType::Identifier(_) => Ok(ast::ExprNode::Variable { TokenType::Identifier(_) => Ok(ast::ExprNode::Variable {
name: self.advance().clone(), name: self.advance().clone(),
}), }),
_ => Err(ParserError::new(self.peek(), "expected expression")), _ => self.error("expected expression"),
} }
} }
} }
@ -718,18 +699,12 @@ impl Parser {
/// call := expression "(" arguments? ")" /// call := expression "(" arguments? ")"
/// arguments := expression ( "," expression )* /// arguments := expression ( "," expression )*
/// ``` /// ```
fn parse_call_arguments( fn parse_call_arguments(&mut self, callee: ast::ExprNode) -> Result<ast::ExprNode, SloxError> {
&mut self,
callee: ast::ExprNode,
) -> Result<ast::ExprNode, ParserError> {
let mut arguments = Vec::new(); let mut arguments = Vec::new();
if !self.check(&TokenType::RightParen) { if !self.check(&TokenType::RightParen) {
loop { loop {
if arguments.len() == 255 { if arguments.len() == 255 {
return Err(ParserError::new( return self.error("functions may not have more than 255 arguments");
self.peek(),
"functions may not have more than 255 arguments",
));
} }
arguments.push(self.parse_expression()?); arguments.push(self.parse_expression()?);
if self.expect(&[TokenType::Comma]).is_none() { if self.expect(&[TokenType::Comma]).is_none() {
@ -764,11 +739,11 @@ impl Parser {
/// Consume a token of a given type. If no matching token is found, a /// Consume a token of a given type. If no matching token is found, a
/// parse error is returned instead. Otherwise the read pointer is moved. /// parse error is returned instead. Otherwise the read pointer is moved.
fn consume(&mut self, token_type: &TokenType, error: &str) -> ParserResult<&Token> { fn consume(&mut self, token_type: &TokenType, error: &str) -> SloxResult<&Token> {
if self.check(token_type) { if self.check(token_type) {
Ok(self.advance()) Ok(self.advance())
} else { } else {
Err(ParserError::new(self.peek(), error)) self.error(error)
} }
} }
@ -841,4 +816,18 @@ impl Parser {
pos -= 1; pos -= 1;
} }
} }
/// Generate an error at the current token.
fn error<O>(&self, message: &str) -> SloxResult<O> {
self.error_mv(message.to_owned())
}
/// Generate an error at the current token.
fn error_mv<O>(&self, message: String) -> SloxResult<O> {
Err(SloxError::with_token(
ErrorKind::Parse,
self.peek(),
message,
))
}
} }