Struct flexi_parse::ParseBuffer

source · 
pub struct ParseBuffer<'a> { /* private fields */ }
Expand description

A cursor position within a token stream.

Implementations§

source§

impl<'a> ParseBuffer<'a>

source

pub fn parse<T: Parse>(&self) -> Result<T>

Attempts to parse self into the given syntax tree node, using T’s default parsing implementation.

Errors

Returns an error if T’s Parse implementation fails.

Examples found in repository?
examples/calc.rs (line 45)
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    fn parse(input: ParseStream) -> Result<Self> {
        let mut expr = factor(input)?;
        loop {
            if input.peek(Punct!["+"]) {
                expr = Expr::Add(Box::new(expr), input.parse()?, Box::new(factor(input)?));
            } else if input.peek(Punct!["-"]) {
                expr = Expr::Sub(Box::new(expr), input.parse()?, Box::new(factor(input)?));
            } else {
                break;
            }
        }
        Ok(expr)
    }
}

fn factor(input: ParseStream) -> Result<Expr> {
    let mut expr: Expr = unary(input)?;
    loop {
        if input.peek(Punct!["*"]) {
            expr = Expr::Mul(Box::new(expr), input.parse()?, Box::new(unary(input)?));
        } else if input.peek(Punct!["/"]) {
            expr = Expr::Div(Box::new(expr), input.parse()?, Box::new(unary(input)?));
        } else if input.peek(Punct!["%"]) {
            expr = Expr::Mod(Box::new(expr), input.parse()?, Box::new(unary(input)?));
        } else {
            break;
        }
    }
    Ok(expr)
}

fn unary(input: ParseStream) -> Result<Expr> {
    if input.peek(Punct!["-"]) {
        Ok(Expr::Neg(input.parse()?, Box::new(unary(input)?)))
    } else {
        primary(input)
    }
}

#[allow(clippy::cast_precision_loss)]
fn primary(input: ParseStream) -> Result<Expr> {
    let lookahead = input.lookahead();
    if lookahead.peek(token::LitFloat) {
        Ok(Expr::Num(input.parse::<token::LitFloat>()?.value()))
    } else if lookahead.peek(token::LitInt) {
        Ok(Expr::Num(input.parse::<token::LitInt>()?.value() as f64))
    } else if lookahead.peek(token::LeftParen) {
        let group: Group<Parentheses> = input.parse()?;
        parse(group.into_token_stream())
    } else {
        Err(lookahead.error())
    }
}
More examples
Hide additional examples
examples/lox/main.rs (line 196)
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    fn assignment(input: ParseStream) -> Result<Self> {
        let expr = Expr::or(input)?;

        if input.peek(Punct!["="]) {
            let equals: Punct!["="] = input.parse()?;
            let value = Box::new(Expr::assignment(input)?);

            if let Expr::Variable { name, .. } = expr {
                return Ok(Expr::Assign {
                    name,
                    value,
                    distance: Cell::new(None),
                });
            } else if let Expr::Get { object, name } = expr {
                return Ok(Expr::Set {
                    object,
                    name,
                    value,
                });
            }

            input.add_error(input.new_error(
                "Invalid assignment target".to_string(),
                &equals,
                error_codes::INVALID_ASSIGN,
            ));
        }

        Ok(expr)
    }

    fn or(input: ParseStream) -> Result<Self> {
        let mut expr = Expr::and(input)?;

        while input.peek(kw::or) {
            expr = Expr::Logical(Box::new(Logical::Or(
                expr,
                input.parse()?,
                Expr::and(input)?,
            )));
        }

        Ok(expr)
    }

    fn and(input: ParseStream) -> Result<Self> {
        let mut expr = Expr::equality(input)?;

        while input.peek(kw::and) {
            expr = Expr::Logical(Box::new(Logical::And(
                expr,
                input.parse()?,
                Expr::equality(input)?,
            )));
        }

        Ok(expr)
    }

    fn equality(input: ParseStream) -> Result<Self> {
        let mut expr = Expr::comparison(input)?;

        loop {
            if input.peek(Punct!["=="]) {
                expr = Expr::binary(Binary::Equal(
                    expr,
                    input.parse()?,
                    Expr::comparison(input)?,
                ));
            } else if input.peek(Punct!["!="]) {
                expr = Expr::binary(Binary::NotEqual(
                    expr,
                    input.parse()?,
                    Expr::comparison(input)?,
                ));
            } else {
                break Ok(expr);
            }
        }
    }

    fn comparison(input: ParseStream) -> Result<Self> {
        let mut expr = Expr::term(input)?;

        loop {
            if input.peek(Punct![">"]) {
                expr = Expr::binary(Binary::Greater(expr, input.parse()?, Expr::term(input)?));
            } else if input.peek(Punct![">="]) {
                expr = Expr::binary(Binary::GreaterEqual(
                    expr,
                    input.parse()?,
                    Expr::term(input)?,
                ));
            } else if input.peek(Punct!["<"]) {
                expr = Expr::binary(Binary::Less(expr, input.parse()?, Expr::term(input)?));
            } else if input.peek(Punct!["<="]) {
                expr = Expr::binary(Binary::LessEqual(expr, input.parse()?, Expr::term(input)?));
            } else {
                break Ok(expr);
            }
        }
    }

    fn term(input: ParseStream) -> Result<Self> {
        let mut expr = Expr::factor(input)?;

        loop {
            if input.peek(Punct!["+"]) {
                expr = Expr::binary(Binary::Add(expr, input.parse()?, Expr::factor(input)?));
            } else if input.peek(Punct!["-"]) {
                expr = Expr::binary(Binary::Sub(expr, input.parse()?, Expr::factor(input)?));
            } else {
                break Ok(expr);
            }
        }
    }

    fn factor(input: ParseStream) -> Result<Self> {
        let mut expr = Expr::unary(input)?;

        loop {
            if input.peek(Punct!["*"]) {
                expr = Expr::binary(Binary::Mul(expr, input.parse()?, Expr::unary(input)?));
            } else if input.peek(Punct!["/"]) {
                expr = Expr::binary(Binary::Div(expr, input.parse()?, Expr::unary(input)?));
            } else {
                break Ok(expr);
            }
        }
    }

    fn unary(input: ParseStream) -> Result<Self> {
        if input.peek(Punct!["-"]) {
            Ok(Expr::Unary(Box::new(Unary::Neg(
                input.parse()?,
                Expr::unary(input)?,
            ))))
        } else if input.peek(Punct!["!"]) {
            Ok(Expr::Unary(Box::new(Unary::Not(
                input.parse()?,
                Expr::unary(input)?,
            ))))
        } else {
            Expr::call(input)
        }
    }

    fn call(input: ParseStream) -> Result<Self> {
        let mut expr = Expr::primary(input)?;

        loop {
            if input.peek(Punct!["("]) {
                expr = Expr::finish_call(input, expr)?;
            } else if input.peek(Punct!["."]) {
                let _: Punct!["."] = input.parse()?;
                let name: Ident = input.parse()?;
                expr = Expr::Get {
                    object: Box::new(expr),
                    name,
                };
            } else {
                break Ok(expr);
            }
        }
    }

    fn finish_call(input: ParseStream<'_>, callee: Expr) -> Result<Self> {
        let content;
        let paren: Parentheses = group!(content in input);
        let arguments: Punctuated<Expr, Punct![","]> =
            Punctuated::parse_separated_trailing(&content)?;
        let arguments: Vec<_> = arguments.into_iter().collect();
        if arguments.len() >= 255 {
            input.add_error(input.new_error(
                "Can't have more than 254 arguments".to_string(),
                paren.0.clone(),
                error_codes::TOO_MANY_ARGS,
            ));
        }
        Ok(Expr::Call {
            callee: Box::new(callee),
            paren,
            arguments,
        })
    }

    fn primary(input: ParseStream) -> Result<Self> {
        let lookahead = input.lookahead();
        if lookahead.peek(kw::kw_false) {
            Ok(Expr::Literal(Literal::False(input.parse()?)))
        } else if lookahead.peek(kw::kw_true) {
            Ok(Expr::Literal(Literal::True(input.parse()?)))
        } else if lookahead.peek(kw::nil) {
            Ok(Expr::Literal(Literal::Nil(input.parse()?)))
        } else if lookahead.peek(LitFloat) {
            Ok(Expr::Literal(Literal::Float(input.parse()?)))
        } else if lookahead.peek(LitInt) {
            Ok(Expr::Literal(Literal::Int(input.parse()?)))
        } else if lookahead.peek(LitStr) {
            Ok(Expr::Literal(Literal::String(input.parse()?)))
        } else if input.peek(kw::kw_super) {
            Ok(Expr::Super {
                keyword: input.parse()?,
                distance: Cell::new(None),
                dot: input.parse()?,
                method: kw::ident(input)?,
            })
        } else if input.peek(kw::this) {
            Ok(Expr::This {
                keyword: input.parse()?,
                distance: Cell::new(None),
            })
        } else if lookahead.peek(Ident) {
            Ok(Expr::Variable {
                name: kw::ident(input)?,
                distance: Cell::new(None),
            })
        } else if lookahead.peek(Punct!["("]) {
            let content;
            let _: Parentheses = group!(content in input);
            Ok(Expr::Group(Box::new(content.parse()?)))
        } else {
            Err(lookahead.error())
        }
    }
}

impl Parse for Expr {
    fn parse(input: ParseStream) -> Result<Self> {
        Expr::assignment(input)
    }
}

#[derive(Debug, Clone, PartialEq)]
struct Function {
    name: Ident,
    params: Vec<Ident>,
    body: Vec<Stmt>,
}

impl Parse for Function {
    fn parse(input: ParseStream) -> Result<Self> {
        let name: Ident = input.parse()?;
        let mut contents: Group<Parentheses> = input.parse()?;
        contents.remove_whitespace();
        let Parentheses(span) = contents.delimiters();
        let tokens = contents.into_token_stream();
        let params: Vec<Ident> = if tokens.is_empty() {
            vec![]
        } else {
            let params: Punctuated<Ident, Punct![","]> =
                Punctuated::parse_separated.parse(tokens)?;
            params.into_iter().collect()
        };
        if params.len() >= 255 {
            input.add_error(input.new_error(
                "Can't have more than 254 parameters".to_string(),
                span,
                error_codes::TOO_MANY_ARGS,
            ));
        }
        let mut contents: Group<Braces> = input.parse()?;
        contents.remove_whitespace();
        let body = block.parse(contents.into_token_stream())?;
        Ok(Function { name, params, body })
    }
}

#[derive(Debug, Clone, PartialEq)]
enum Stmt {
    Block(Vec<Stmt>),
    Class {
        name: Ident,
        superclass: Option<Ident>,
        superclass_distance: Cell<Option<usize>>,
        methods: Vec<Function>,
    },
    Expr(Expr),
    Function(Function),
    If {
        condition: Expr,
        then_branch: Box<Stmt>,
        else_branch: Option<Box<Stmt>>,
    },
    Print(Expr),
    Return {
        keyword: kw::kw_return,
        value: Option<Expr>,
    },
    Variable {
        name: Ident,
        initialiser: Option<Expr>,
    },
    While {
        condition: Expr,
        body: Box<Stmt>,
    },
}

fn block(input: ParseStream) -> Result<Vec<Stmt>> {
    let mut statements = vec![];

    while !input.is_empty() {
        statements.push(Stmt::declaration(input)?);
    }

    Ok(statements)
}

impl Stmt {
    fn declaration(input: ParseStream) -> Result<Self> {
        if input.peek(kw::class) {
            Stmt::class_declaration(input)
        } else if input.peek(kw::fun) {
            let _: kw::fun = input.parse()?;
            Ok(Stmt::Function(Function::parse(input)?))
        } else if input.peek(kw::var) {
            Stmt::var_declaration(input)
        } else {
            Stmt::statement(input)
        }
    }

    fn class_declaration(input: ParseStream) -> Result<Self> {
        let _: kw::class = input.parse()?;
        let name: Ident = input.parse()?;

        let superclass = if input.peek(Punct!["<"]) {
            let _: Punct!["<"] = input.parse()?;
            Some(input.parse()?)
        } else {
            None
        };

        let content;
        let _: Braces = group!(content in input);
        let methods = parse_repeated(&content)?;

        Ok(Stmt::Class {
            name,
            superclass,
            superclass_distance: Cell::new(None),
            methods,
        })
    }

    fn var_declaration(input: ParseStream) -> Result<Self> {
        let _: kw::var = input.parse()?;

        let name = kw::ident(input)?;

        let initialiser = if input.peek(Punct!["="]) {
            let _: Punct!["="] = input.parse()?;
            Some(input.parse()?)
        } else {
            None
        };

        let _: Punct![";"] = input.parse()?;
        Ok(Stmt::Variable { name, initialiser })
    }

    fn statement(input: ParseStream) -> Result<Self> {
        if input.peek(kw::kw_if) {
            Stmt::if_statement(input)
        } else if input.peek(kw::kw_for) {
            Stmt::for_statement(input)
        } else if input.peek(kw::print) {
            Stmt::print_statement(input)
        } else if input.peek(kw::kw_return) {
            Stmt::return_statement(input)
        } else if input.peek(kw::kw_while) {
            Stmt::while_statement(input)
        } else if input.peek(Punct!["{"]) {
            let content;
            let _: Braces = group!(content in input);
            Ok(Stmt::Block(block(&content)?))
        } else {
            Stmt::expression_statement(input)
        }
    }

    fn for_statement(input: ParseStream) -> Result<Self> {
        let _: kw::kw_for = input.parse()?;

        let content;
        let _: Parentheses = group!(content in input);

        let initialiser = if content.peek(Punct![";"]) {
            let _: Punct![";"] = content.parse()?;
            None
        } else if content.peek(kw::var) {
            Some(Stmt::var_declaration(&content)?)
        } else {
            Some(Stmt::expression_statement(&content)?)
        };

        let condition = if content.peek(Punct![";"]) {
            Expr::Literal(Literal::True(kw::kw_true::new(&content)))
        } else {
            content.parse()?
        };
        let _: Punct![";"] = content.parse()?;

        let increment = if content.is_empty() {
            None
        } else {
            Some(content.parse()?)
        };

        let mut body = Stmt::statement(input)?;

        if let Some(increment) = increment {
            body = Stmt::Block(vec![body, Stmt::Expr(increment)]);
        }

        body = Stmt::While {
            condition,
            body: Box::new(body),
        };

        if let Some(initialiser) = initialiser {
            body = Stmt::Block(vec![initialiser, body]);
        }

        Ok(body)
    }

    fn if_statement(input: ParseStream) -> Result<Self> {
        let _: kw::kw_if = input.parse()?;
        let content;
        let _: Parentheses = group!(content in input);
        let condition = content.parse()?;

        let then_branch = Box::new(Stmt::statement(input)?);
        let else_branch = if input.peek(kw::kw_else) {
            Some(Box::new(Stmt::statement(input)?))
        } else {
            None
        };

        Ok(Stmt::If {
            condition,
            then_branch,
            else_branch,
        })
    }

    fn print_statement(input: ParseStream) -> Result<Self> {
        let _: kw::print = input.parse()?;
        let value = input.parse()?;
        let _: Punct![";"] = input.parse()?;
        Ok(Self::Print(value))
    }

    fn return_statement(input: ParseStream) -> Result<Self> {
        let keyword: kw::kw_return = input.parse()?;
        let value = if input.peek(Punct![";"]) {
            None
        } else {
            Some(input.parse()?)
        };
        let _: Punct![";"] = input.parse()?;
        Ok(Stmt::Return { keyword, value })
    }

    fn while_statement(input: ParseStream) -> Result<Self> {
        let _: kw::kw_while = input.parse()?;
        let content;
        let _: Parentheses = group!(content in input);
        let condition = content.parse()?;
        let body = Box::new(Stmt::statement(input)?);

        Ok(Stmt::While { condition, body })
    }

    fn expression_statement(input: ParseStream) -> Result<Self> {
        let expr = input.parse()?;
        let _: Punct![";"] = input.parse()?;
        Ok(Self::Expr(expr))
    }
}

impl Parse for Stmt {
    fn parse(input: ParseStream) -> Result<Self> {
        Stmt::declaration(input)
    }
}

struct Ast(Vec<Stmt>);

impl Ast {
    #[allow(clippy::wildcard_imports)]
    fn synchronise(input: ParseStream) {
        input.synchronise(|input| {
            use kw::*;
            input.peek(Punct![";"]) && !input.peek2(Punct!["}"])
                || peek2_any!(input, class, kw_for, fun, kw_if, print, kw_return, var, kw_while)
        });
    }
}

impl Parse for Ast {
    fn parse(input: ParseStream) -> Result<Self> {
        let mut stmts = vec![];

        while !input.is_empty() {
            match input.parse() {
                Ok(stmt) => stmts.push(stmt),
                Err(err) => {
                    Ast::synchronise(input);
                    input.add_error(err);
                }
            }
        }

        input.get_error().map_or(Ok(Ast(stmts)), Err)
    }
source

pub fn is_empty(&self) -> bool

Returns true if this stream has been exhausted.

Examples found in repository?
examples/lox/main.rs (line 494)
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fn block(input: ParseStream) -> Result<Vec<Stmt>> {
    let mut statements = vec![];

    while !input.is_empty() {
        statements.push(Stmt::declaration(input)?);
    }

    Ok(statements)
}

impl Stmt {
    fn declaration(input: ParseStream) -> Result<Self> {
        if input.peek(kw::class) {
            Stmt::class_declaration(input)
        } else if input.peek(kw::fun) {
            let _: kw::fun = input.parse()?;
            Ok(Stmt::Function(Function::parse(input)?))
        } else if input.peek(kw::var) {
            Stmt::var_declaration(input)
        } else {
            Stmt::statement(input)
        }
    }

    fn class_declaration(input: ParseStream) -> Result<Self> {
        let _: kw::class = input.parse()?;
        let name: Ident = input.parse()?;

        let superclass = if input.peek(Punct!["<"]) {
            let _: Punct!["<"] = input.parse()?;
            Some(input.parse()?)
        } else {
            None
        };

        let content;
        let _: Braces = group!(content in input);
        let methods = parse_repeated(&content)?;

        Ok(Stmt::Class {
            name,
            superclass,
            superclass_distance: Cell::new(None),
            methods,
        })
    }

    fn var_declaration(input: ParseStream) -> Result<Self> {
        let _: kw::var = input.parse()?;

        let name = kw::ident(input)?;

        let initialiser = if input.peek(Punct!["="]) {
            let _: Punct!["="] = input.parse()?;
            Some(input.parse()?)
        } else {
            None
        };

        let _: Punct![";"] = input.parse()?;
        Ok(Stmt::Variable { name, initialiser })
    }

    fn statement(input: ParseStream) -> Result<Self> {
        if input.peek(kw::kw_if) {
            Stmt::if_statement(input)
        } else if input.peek(kw::kw_for) {
            Stmt::for_statement(input)
        } else if input.peek(kw::print) {
            Stmt::print_statement(input)
        } else if input.peek(kw::kw_return) {
            Stmt::return_statement(input)
        } else if input.peek(kw::kw_while) {
            Stmt::while_statement(input)
        } else if input.peek(Punct!["{"]) {
            let content;
            let _: Braces = group!(content in input);
            Ok(Stmt::Block(block(&content)?))
        } else {
            Stmt::expression_statement(input)
        }
    }

    fn for_statement(input: ParseStream) -> Result<Self> {
        let _: kw::kw_for = input.parse()?;

        let content;
        let _: Parentheses = group!(content in input);

        let initialiser = if content.peek(Punct![";"]) {
            let _: Punct![";"] = content.parse()?;
            None
        } else if content.peek(kw::var) {
            Some(Stmt::var_declaration(&content)?)
        } else {
            Some(Stmt::expression_statement(&content)?)
        };

        let condition = if content.peek(Punct![";"]) {
            Expr::Literal(Literal::True(kw::kw_true::new(&content)))
        } else {
            content.parse()?
        };
        let _: Punct![";"] = content.parse()?;

        let increment = if content.is_empty() {
            None
        } else {
            Some(content.parse()?)
        };

        let mut body = Stmt::statement(input)?;

        if let Some(increment) = increment {
            body = Stmt::Block(vec![body, Stmt::Expr(increment)]);
        }

        body = Stmt::While {
            condition,
            body: Box::new(body),
        };

        if let Some(initialiser) = initialiser {
            body = Stmt::Block(vec![initialiser, body]);
        }

        Ok(body)
    }

    fn if_statement(input: ParseStream) -> Result<Self> {
        let _: kw::kw_if = input.parse()?;
        let content;
        let _: Parentheses = group!(content in input);
        let condition = content.parse()?;

        let then_branch = Box::new(Stmt::statement(input)?);
        let else_branch = if input.peek(kw::kw_else) {
            Some(Box::new(Stmt::statement(input)?))
        } else {
            None
        };

        Ok(Stmt::If {
            condition,
            then_branch,
            else_branch,
        })
    }

    fn print_statement(input: ParseStream) -> Result<Self> {
        let _: kw::print = input.parse()?;
        let value = input.parse()?;
        let _: Punct![";"] = input.parse()?;
        Ok(Self::Print(value))
    }

    fn return_statement(input: ParseStream) -> Result<Self> {
        let keyword: kw::kw_return = input.parse()?;
        let value = if input.peek(Punct![";"]) {
            None
        } else {
            Some(input.parse()?)
        };
        let _: Punct![";"] = input.parse()?;
        Ok(Stmt::Return { keyword, value })
    }

    fn while_statement(input: ParseStream) -> Result<Self> {
        let _: kw::kw_while = input.parse()?;
        let content;
        let _: Parentheses = group!(content in input);
        let condition = content.parse()?;
        let body = Box::new(Stmt::statement(input)?);

        Ok(Stmt::While { condition, body })
    }

    fn expression_statement(input: ParseStream) -> Result<Self> {
        let expr = input.parse()?;
        let _: Punct![";"] = input.parse()?;
        Ok(Self::Expr(expr))
    }
}

impl Parse for Stmt {
    fn parse(input: ParseStream) -> Result<Self> {
        Stmt::declaration(input)
    }
}

struct Ast(Vec<Stmt>);

impl Ast {
    #[allow(clippy::wildcard_imports)]
    fn synchronise(input: ParseStream) {
        input.synchronise(|input| {
            use kw::*;
            input.peek(Punct![";"]) && !input.peek2(Punct!["}"])
                || peek2_any!(input, class, kw_for, fun, kw_if, print, kw_return, var, kw_while)
        });
    }
}

impl Parse for Ast {
    fn parse(input: ParseStream) -> Result<Self> {
        let mut stmts = vec![];

        while !input.is_empty() {
            match input.parse() {
                Ok(stmt) => stmts.push(stmt),
                Err(err) => {
                    Ast::synchronise(input);
                    input.add_error(err);
                }
            }
        }

        input.get_error().map_or(Ok(Ast(stmts)), Err)
    }
source

pub fn new_error<T: Into<Span>>( &self, message: String, location: T, code: u16 ) -> Error

Creates a new error at the given location with the given message and code.

Examples found in repository?
examples/lox/main.rs (lines 213-217)
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    fn assignment(input: ParseStream) -> Result<Self> {
        let expr = Expr::or(input)?;

        if input.peek(Punct!["="]) {
            let equals: Punct!["="] = input.parse()?;
            let value = Box::new(Expr::assignment(input)?);

            if let Expr::Variable { name, .. } = expr {
                return Ok(Expr::Assign {
                    name,
                    value,
                    distance: Cell::new(None),
                });
            } else if let Expr::Get { object, name } = expr {
                return Ok(Expr::Set {
                    object,
                    name,
                    value,
                });
            }

            input.add_error(input.new_error(
                "Invalid assignment target".to_string(),
                &equals,
                error_codes::INVALID_ASSIGN,
            ));
        }

        Ok(expr)
    }

    fn or(input: ParseStream) -> Result<Self> {
        let mut expr = Expr::and(input)?;

        while input.peek(kw::or) {
            expr = Expr::Logical(Box::new(Logical::Or(
                expr,
                input.parse()?,
                Expr::and(input)?,
            )));
        }

        Ok(expr)
    }

    fn and(input: ParseStream) -> Result<Self> {
        let mut expr = Expr::equality(input)?;

        while input.peek(kw::and) {
            expr = Expr::Logical(Box::new(Logical::And(
                expr,
                input.parse()?,
                Expr::equality(input)?,
            )));
        }

        Ok(expr)
    }

    fn equality(input: ParseStream) -> Result<Self> {
        let mut expr = Expr::comparison(input)?;

        loop {
            if input.peek(Punct!["=="]) {
                expr = Expr::binary(Binary::Equal(
                    expr,
                    input.parse()?,
                    Expr::comparison(input)?,
                ));
            } else if input.peek(Punct!["!="]) {
                expr = Expr::binary(Binary::NotEqual(
                    expr,
                    input.parse()?,
                    Expr::comparison(input)?,
                ));
            } else {
                break Ok(expr);
            }
        }
    }

    fn comparison(input: ParseStream) -> Result<Self> {
        let mut expr = Expr::term(input)?;

        loop {
            if input.peek(Punct![">"]) {
                expr = Expr::binary(Binary::Greater(expr, input.parse()?, Expr::term(input)?));
            } else if input.peek(Punct![">="]) {
                expr = Expr::binary(Binary::GreaterEqual(
                    expr,
                    input.parse()?,
                    Expr::term(input)?,
                ));
            } else if input.peek(Punct!["<"]) {
                expr = Expr::binary(Binary::Less(expr, input.parse()?, Expr::term(input)?));
            } else if input.peek(Punct!["<="]) {
                expr = Expr::binary(Binary::LessEqual(expr, input.parse()?, Expr::term(input)?));
            } else {
                break Ok(expr);
            }
        }
    }

    fn term(input: ParseStream) -> Result<Self> {
        let mut expr = Expr::factor(input)?;

        loop {
            if input.peek(Punct!["+"]) {
                expr = Expr::binary(Binary::Add(expr, input.parse()?, Expr::factor(input)?));
            } else if input.peek(Punct!["-"]) {
                expr = Expr::binary(Binary::Sub(expr, input.parse()?, Expr::factor(input)?));
            } else {
                break Ok(expr);
            }
        }
    }

    fn factor(input: ParseStream) -> Result<Self> {
        let mut expr = Expr::unary(input)?;

        loop {
            if input.peek(Punct!["*"]) {
                expr = Expr::binary(Binary::Mul(expr, input.parse()?, Expr::unary(input)?));
            } else if input.peek(Punct!["/"]) {
                expr = Expr::binary(Binary::Div(expr, input.parse()?, Expr::unary(input)?));
            } else {
                break Ok(expr);
            }
        }
    }

    fn unary(input: ParseStream) -> Result<Self> {
        if input.peek(Punct!["-"]) {
            Ok(Expr::Unary(Box::new(Unary::Neg(
                input.parse()?,
                Expr::unary(input)?,
            ))))
        } else if input.peek(Punct!["!"]) {
            Ok(Expr::Unary(Box::new(Unary::Not(
                input.parse()?,
                Expr::unary(input)?,
            ))))
        } else {
            Expr::call(input)
        }
    }

    fn call(input: ParseStream) -> Result<Self> {
        let mut expr = Expr::primary(input)?;

        loop {
            if input.peek(Punct!["("]) {
                expr = Expr::finish_call(input, expr)?;
            } else if input.peek(Punct!["."]) {
                let _: Punct!["."] = input.parse()?;
                let name: Ident = input.parse()?;
                expr = Expr::Get {
                    object: Box::new(expr),
                    name,
                };
            } else {
                break Ok(expr);
            }
        }
    }

    fn finish_call(input: ParseStream<'_>, callee: Expr) -> Result<Self> {
        let content;
        let paren: Parentheses = group!(content in input);
        let arguments: Punctuated<Expr, Punct![","]> =
            Punctuated::parse_separated_trailing(&content)?;
        let arguments: Vec<_> = arguments.into_iter().collect();
        if arguments.len() >= 255 {
            input.add_error(input.new_error(
                "Can't have more than 254 arguments".to_string(),
                paren.0.clone(),
                error_codes::TOO_MANY_ARGS,
            ));
        }
        Ok(Expr::Call {
            callee: Box::new(callee),
            paren,
            arguments,
        })
    }

    fn primary(input: ParseStream) -> Result<Self> {
        let lookahead = input.lookahead();
        if lookahead.peek(kw::kw_false) {
            Ok(Expr::Literal(Literal::False(input.parse()?)))
        } else if lookahead.peek(kw::kw_true) {
            Ok(Expr::Literal(Literal::True(input.parse()?)))
        } else if lookahead.peek(kw::nil) {
            Ok(Expr::Literal(Literal::Nil(input.parse()?)))
        } else if lookahead.peek(LitFloat) {
            Ok(Expr::Literal(Literal::Float(input.parse()?)))
        } else if lookahead.peek(LitInt) {
            Ok(Expr::Literal(Literal::Int(input.parse()?)))
        } else if lookahead.peek(LitStr) {
            Ok(Expr::Literal(Literal::String(input.parse()?)))
        } else if input.peek(kw::kw_super) {
            Ok(Expr::Super {
                keyword: input.parse()?,
                distance: Cell::new(None),
                dot: input.parse()?,
                method: kw::ident(input)?,
            })
        } else if input.peek(kw::this) {
            Ok(Expr::This {
                keyword: input.parse()?,
                distance: Cell::new(None),
            })
        } else if lookahead.peek(Ident) {
            Ok(Expr::Variable {
                name: kw::ident(input)?,
                distance: Cell::new(None),
            })
        } else if lookahead.peek(Punct!["("]) {
            let content;
            let _: Parentheses = group!(content in input);
            Ok(Expr::Group(Box::new(content.parse()?)))
        } else {
            Err(lookahead.error())
        }
    }
}

impl Parse for Expr {
    fn parse(input: ParseStream) -> Result<Self> {
        Expr::assignment(input)
    }
}

#[derive(Debug, Clone, PartialEq)]
struct Function {
    name: Ident,
    params: Vec<Ident>,
    body: Vec<Stmt>,
}

impl Parse for Function {
    fn parse(input: ParseStream) -> Result<Self> {
        let name: Ident = input.parse()?;
        let mut contents: Group<Parentheses> = input.parse()?;
        contents.remove_whitespace();
        let Parentheses(span) = contents.delimiters();
        let tokens = contents.into_token_stream();
        let params: Vec<Ident> = if tokens.is_empty() {
            vec![]
        } else {
            let params: Punctuated<Ident, Punct![","]> =
                Punctuated::parse_separated.parse(tokens)?;
            params.into_iter().collect()
        };
        if params.len() >= 255 {
            input.add_error(input.new_error(
                "Can't have more than 254 parameters".to_string(),
                span,
                error_codes::TOO_MANY_ARGS,
            ));
        }
        let mut contents: Group<Braces> = input.parse()?;
        contents.remove_whitespace();
        let body = block.parse(contents.into_token_stream())?;
        Ok(Function { name, params, body })
    }
source

pub fn add_error(&self, error: Error)

Adds a new error to this buffer’s storage.

Examples found in repository?
examples/lox/main.rs (lines 213-217)
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    fn assignment(input: ParseStream) -> Result<Self> {
        let expr = Expr::or(input)?;

        if input.peek(Punct!["="]) {
            let equals: Punct!["="] = input.parse()?;
            let value = Box::new(Expr::assignment(input)?);

            if let Expr::Variable { name, .. } = expr {
                return Ok(Expr::Assign {
                    name,
                    value,
                    distance: Cell::new(None),
                });
            } else if let Expr::Get { object, name } = expr {
                return Ok(Expr::Set {
                    object,
                    name,
                    value,
                });
            }

            input.add_error(input.new_error(
                "Invalid assignment target".to_string(),
                &equals,
                error_codes::INVALID_ASSIGN,
            ));
        }

        Ok(expr)
    }

    fn or(input: ParseStream) -> Result<Self> {
        let mut expr = Expr::and(input)?;

        while input.peek(kw::or) {
            expr = Expr::Logical(Box::new(Logical::Or(
                expr,
                input.parse()?,
                Expr::and(input)?,
            )));
        }

        Ok(expr)
    }

    fn and(input: ParseStream) -> Result<Self> {
        let mut expr = Expr::equality(input)?;

        while input.peek(kw::and) {
            expr = Expr::Logical(Box::new(Logical::And(
                expr,
                input.parse()?,
                Expr::equality(input)?,
            )));
        }

        Ok(expr)
    }

    fn equality(input: ParseStream) -> Result<Self> {
        let mut expr = Expr::comparison(input)?;

        loop {
            if input.peek(Punct!["=="]) {
                expr = Expr::binary(Binary::Equal(
                    expr,
                    input.parse()?,
                    Expr::comparison(input)?,
                ));
            } else if input.peek(Punct!["!="]) {
                expr = Expr::binary(Binary::NotEqual(
                    expr,
                    input.parse()?,
                    Expr::comparison(input)?,
                ));
            } else {
                break Ok(expr);
            }
        }
    }

    fn comparison(input: ParseStream) -> Result<Self> {
        let mut expr = Expr::term(input)?;

        loop {
            if input.peek(Punct![">"]) {
                expr = Expr::binary(Binary::Greater(expr, input.parse()?, Expr::term(input)?));
            } else if input.peek(Punct![">="]) {
                expr = Expr::binary(Binary::GreaterEqual(
                    expr,
                    input.parse()?,
                    Expr::term(input)?,
                ));
            } else if input.peek(Punct!["<"]) {
                expr = Expr::binary(Binary::Less(expr, input.parse()?, Expr::term(input)?));
            } else if input.peek(Punct!["<="]) {
                expr = Expr::binary(Binary::LessEqual(expr, input.parse()?, Expr::term(input)?));
            } else {
                break Ok(expr);
            }
        }
    }

    fn term(input: ParseStream) -> Result<Self> {
        let mut expr = Expr::factor(input)?;

        loop {
            if input.peek(Punct!["+"]) {
                expr = Expr::binary(Binary::Add(expr, input.parse()?, Expr::factor(input)?));
            } else if input.peek(Punct!["-"]) {
                expr = Expr::binary(Binary::Sub(expr, input.parse()?, Expr::factor(input)?));
            } else {
                break Ok(expr);
            }
        }
    }

    fn factor(input: ParseStream) -> Result<Self> {
        let mut expr = Expr::unary(input)?;

        loop {
            if input.peek(Punct!["*"]) {
                expr = Expr::binary(Binary::Mul(expr, input.parse()?, Expr::unary(input)?));
            } else if input.peek(Punct!["/"]) {
                expr = Expr::binary(Binary::Div(expr, input.parse()?, Expr::unary(input)?));
            } else {
                break Ok(expr);
            }
        }
    }

    fn unary(input: ParseStream) -> Result<Self> {
        if input.peek(Punct!["-"]) {
            Ok(Expr::Unary(Box::new(Unary::Neg(
                input.parse()?,
                Expr::unary(input)?,
            ))))
        } else if input.peek(Punct!["!"]) {
            Ok(Expr::Unary(Box::new(Unary::Not(
                input.parse()?,
                Expr::unary(input)?,
            ))))
        } else {
            Expr::call(input)
        }
    }

    fn call(input: ParseStream) -> Result<Self> {
        let mut expr = Expr::primary(input)?;

        loop {
            if input.peek(Punct!["("]) {
                expr = Expr::finish_call(input, expr)?;
            } else if input.peek(Punct!["."]) {
                let _: Punct!["."] = input.parse()?;
                let name: Ident = input.parse()?;
                expr = Expr::Get {
                    object: Box::new(expr),
                    name,
                };
            } else {
                break Ok(expr);
            }
        }
    }

    fn finish_call(input: ParseStream<'_>, callee: Expr) -> Result<Self> {
        let content;
        let paren: Parentheses = group!(content in input);
        let arguments: Punctuated<Expr, Punct![","]> =
            Punctuated::parse_separated_trailing(&content)?;
        let arguments: Vec<_> = arguments.into_iter().collect();
        if arguments.len() >= 255 {
            input.add_error(input.new_error(
                "Can't have more than 254 arguments".to_string(),
                paren.0.clone(),
                error_codes::TOO_MANY_ARGS,
            ));
        }
        Ok(Expr::Call {
            callee: Box::new(callee),
            paren,
            arguments,
        })
    }

    fn primary(input: ParseStream) -> Result<Self> {
        let lookahead = input.lookahead();
        if lookahead.peek(kw::kw_false) {
            Ok(Expr::Literal(Literal::False(input.parse()?)))
        } else if lookahead.peek(kw::kw_true) {
            Ok(Expr::Literal(Literal::True(input.parse()?)))
        } else if lookahead.peek(kw::nil) {
            Ok(Expr::Literal(Literal::Nil(input.parse()?)))
        } else if lookahead.peek(LitFloat) {
            Ok(Expr::Literal(Literal::Float(input.parse()?)))
        } else if lookahead.peek(LitInt) {
            Ok(Expr::Literal(Literal::Int(input.parse()?)))
        } else if lookahead.peek(LitStr) {
            Ok(Expr::Literal(Literal::String(input.parse()?)))
        } else if input.peek(kw::kw_super) {
            Ok(Expr::Super {
                keyword: input.parse()?,
                distance: Cell::new(None),
                dot: input.parse()?,
                method: kw::ident(input)?,
            })
        } else if input.peek(kw::this) {
            Ok(Expr::This {
                keyword: input.parse()?,
                distance: Cell::new(None),
            })
        } else if lookahead.peek(Ident) {
            Ok(Expr::Variable {
                name: kw::ident(input)?,
                distance: Cell::new(None),
            })
        } else if lookahead.peek(Punct!["("]) {
            let content;
            let _: Parentheses = group!(content in input);
            Ok(Expr::Group(Box::new(content.parse()?)))
        } else {
            Err(lookahead.error())
        }
    }
}

impl Parse for Expr {
    fn parse(input: ParseStream) -> Result<Self> {
        Expr::assignment(input)
    }
}

#[derive(Debug, Clone, PartialEq)]
struct Function {
    name: Ident,
    params: Vec<Ident>,
    body: Vec<Stmt>,
}

impl Parse for Function {
    fn parse(input: ParseStream) -> Result<Self> {
        let name: Ident = input.parse()?;
        let mut contents: Group<Parentheses> = input.parse()?;
        contents.remove_whitespace();
        let Parentheses(span) = contents.delimiters();
        let tokens = contents.into_token_stream();
        let params: Vec<Ident> = if tokens.is_empty() {
            vec![]
        } else {
            let params: Punctuated<Ident, Punct![","]> =
                Punctuated::parse_separated.parse(tokens)?;
            params.into_iter().collect()
        };
        if params.len() >= 255 {
            input.add_error(input.new_error(
                "Can't have more than 254 parameters".to_string(),
                span,
                error_codes::TOO_MANY_ARGS,
            ));
        }
        let mut contents: Group<Braces> = input.parse()?;
        contents.remove_whitespace();
        let body = block.parse(contents.into_token_stream())?;
        Ok(Function { name, params, body })
    }
}

#[derive(Debug, Clone, PartialEq)]
enum Stmt {
    Block(Vec<Stmt>),
    Class {
        name: Ident,
        superclass: Option<Ident>,
        superclass_distance: Cell<Option<usize>>,
        methods: Vec<Function>,
    },
    Expr(Expr),
    Function(Function),
    If {
        condition: Expr,
        then_branch: Box<Stmt>,
        else_branch: Option<Box<Stmt>>,
    },
    Print(Expr),
    Return {
        keyword: kw::kw_return,
        value: Option<Expr>,
    },
    Variable {
        name: Ident,
        initialiser: Option<Expr>,
    },
    While {
        condition: Expr,
        body: Box<Stmt>,
    },
}

fn block(input: ParseStream) -> Result<Vec<Stmt>> {
    let mut statements = vec![];

    while !input.is_empty() {
        statements.push(Stmt::declaration(input)?);
    }

    Ok(statements)
}

impl Stmt {
    fn declaration(input: ParseStream) -> Result<Self> {
        if input.peek(kw::class) {
            Stmt::class_declaration(input)
        } else if input.peek(kw::fun) {
            let _: kw::fun = input.parse()?;
            Ok(Stmt::Function(Function::parse(input)?))
        } else if input.peek(kw::var) {
            Stmt::var_declaration(input)
        } else {
            Stmt::statement(input)
        }
    }

    fn class_declaration(input: ParseStream) -> Result<Self> {
        let _: kw::class = input.parse()?;
        let name: Ident = input.parse()?;

        let superclass = if input.peek(Punct!["<"]) {
            let _: Punct!["<"] = input.parse()?;
            Some(input.parse()?)
        } else {
            None
        };

        let content;
        let _: Braces = group!(content in input);
        let methods = parse_repeated(&content)?;

        Ok(Stmt::Class {
            name,
            superclass,
            superclass_distance: Cell::new(None),
            methods,
        })
    }

    fn var_declaration(input: ParseStream) -> Result<Self> {
        let _: kw::var = input.parse()?;

        let name = kw::ident(input)?;

        let initialiser = if input.peek(Punct!["="]) {
            let _: Punct!["="] = input.parse()?;
            Some(input.parse()?)
        } else {
            None
        };

        let _: Punct![";"] = input.parse()?;
        Ok(Stmt::Variable { name, initialiser })
    }

    fn statement(input: ParseStream) -> Result<Self> {
        if input.peek(kw::kw_if) {
            Stmt::if_statement(input)
        } else if input.peek(kw::kw_for) {
            Stmt::for_statement(input)
        } else if input.peek(kw::print) {
            Stmt::print_statement(input)
        } else if input.peek(kw::kw_return) {
            Stmt::return_statement(input)
        } else if input.peek(kw::kw_while) {
            Stmt::while_statement(input)
        } else if input.peek(Punct!["{"]) {
            let content;
            let _: Braces = group!(content in input);
            Ok(Stmt::Block(block(&content)?))
        } else {
            Stmt::expression_statement(input)
        }
    }

    fn for_statement(input: ParseStream) -> Result<Self> {
        let _: kw::kw_for = input.parse()?;

        let content;
        let _: Parentheses = group!(content in input);

        let initialiser = if content.peek(Punct![";"]) {
            let _: Punct![";"] = content.parse()?;
            None
        } else if content.peek(kw::var) {
            Some(Stmt::var_declaration(&content)?)
        } else {
            Some(Stmt::expression_statement(&content)?)
        };

        let condition = if content.peek(Punct![";"]) {
            Expr::Literal(Literal::True(kw::kw_true::new(&content)))
        } else {
            content.parse()?
        };
        let _: Punct![";"] = content.parse()?;

        let increment = if content.is_empty() {
            None
        } else {
            Some(content.parse()?)
        };

        let mut body = Stmt::statement(input)?;

        if let Some(increment) = increment {
            body = Stmt::Block(vec![body, Stmt::Expr(increment)]);
        }

        body = Stmt::While {
            condition,
            body: Box::new(body),
        };

        if let Some(initialiser) = initialiser {
            body = Stmt::Block(vec![initialiser, body]);
        }

        Ok(body)
    }

    fn if_statement(input: ParseStream) -> Result<Self> {
        let _: kw::kw_if = input.parse()?;
        let content;
        let _: Parentheses = group!(content in input);
        let condition = content.parse()?;

        let then_branch = Box::new(Stmt::statement(input)?);
        let else_branch = if input.peek(kw::kw_else) {
            Some(Box::new(Stmt::statement(input)?))
        } else {
            None
        };

        Ok(Stmt::If {
            condition,
            then_branch,
            else_branch,
        })
    }

    fn print_statement(input: ParseStream) -> Result<Self> {
        let _: kw::print = input.parse()?;
        let value = input.parse()?;
        let _: Punct![";"] = input.parse()?;
        Ok(Self::Print(value))
    }

    fn return_statement(input: ParseStream) -> Result<Self> {
        let keyword: kw::kw_return = input.parse()?;
        let value = if input.peek(Punct![";"]) {
            None
        } else {
            Some(input.parse()?)
        };
        let _: Punct![";"] = input.parse()?;
        Ok(Stmt::Return { keyword, value })
    }

    fn while_statement(input: ParseStream) -> Result<Self> {
        let _: kw::kw_while = input.parse()?;
        let content;
        let _: Parentheses = group!(content in input);
        let condition = content.parse()?;
        let body = Box::new(Stmt::statement(input)?);

        Ok(Stmt::While { condition, body })
    }

    fn expression_statement(input: ParseStream) -> Result<Self> {
        let expr = input.parse()?;
        let _: Punct![";"] = input.parse()?;
        Ok(Self::Expr(expr))
    }
}

impl Parse for Stmt {
    fn parse(input: ParseStream) -> Result<Self> {
        Stmt::declaration(input)
    }
}

struct Ast(Vec<Stmt>);

impl Ast {
    #[allow(clippy::wildcard_imports)]
    fn synchronise(input: ParseStream) {
        input.synchronise(|input| {
            use kw::*;
            input.peek(Punct![";"]) && !input.peek2(Punct!["}"])
                || peek2_any!(input, class, kw_for, fun, kw_if, print, kw_return, var, kw_while)
        });
    }
}

impl Parse for Ast {
    fn parse(input: ParseStream) -> Result<Self> {
        let mut stmts = vec![];

        while !input.is_empty() {
            match input.parse() {
                Ok(stmt) => stmts.push(stmt),
                Err(err) => {
                    Ast::synchronise(input);
                    input.add_error(err);
                }
            }
        }

        input.get_error().map_or(Ok(Ast(stmts)), Err)
    }
source

pub fn get_error(&self) -> Option<Error>

Returns an error consisting of all errors from ParseBuffer::add_error, if it has been called.

Examples found in repository?
examples/lox/main.rs (line 708)
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    fn parse(input: ParseStream) -> Result<Self> {
        let mut stmts = vec![];

        while !input.is_empty() {
            match input.parse() {
                Ok(stmt) => stmts.push(stmt),
                Err(err) => {
                    Ast::synchronise(input);
                    input.add_error(err);
                }
            }
        }

        input.get_error().map_or(Ok(Ast(stmts)), Err)
    }
source

pub fn synchronise<F: FnMut(ParseStream<'_>) -> bool>(&self, function: F)

Repeatedly skips tokens until function returns true or self is empty.

Examples found in repository?
examples/lox/main.rs (lines 686-690)
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    fn synchronise(input: ParseStream) {
        input.synchronise(|input| {
            use kw::*;
            input.peek(Punct![";"]) && !input.peek2(Punct!["}"])
                || peek2_any!(input, class, kw_for, fun, kw_if, print, kw_return, var, kw_while)
        });
    }
source

pub fn parse_joint<T1: Token, T2: Token>(&self) -> Result<(T1, T2)>

Parses T1 and T2, with no whitespace allowed between them.

Errors

Returns an error if self does not start with the required tokens.

source

pub fn parse_repeated<T: Parse>(&self) -> Result<Vec<T>>

Attempts to parse self into Vec<T>, with no separating punctuation, fully consuming self.

To parse separated instances of T, see Punctuated.

Errors

Returns an error if self is not a valid sequence of T.

source

pub fn peek<T: Peek>(&self, token: T) -> bool

Returns true if the next token is an instance of T.

Examples found in repository?
examples/calc.rs (line 44)
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    fn parse(input: ParseStream) -> Result<Self> {
        let mut expr = factor(input)?;
        loop {
            if input.peek(Punct!["+"]) {
                expr = Expr::Add(Box::new(expr), input.parse()?, Box::new(factor(input)?));
            } else if input.peek(Punct!["-"]) {
                expr = Expr::Sub(Box::new(expr), input.parse()?, Box::new(factor(input)?));
            } else {
                break;
            }
        }
        Ok(expr)
    }
}

fn factor(input: ParseStream) -> Result<Expr> {
    let mut expr: Expr = unary(input)?;
    loop {
        if input.peek(Punct!["*"]) {
            expr = Expr::Mul(Box::new(expr), input.parse()?, Box::new(unary(input)?));
        } else if input.peek(Punct!["/"]) {
            expr = Expr::Div(Box::new(expr), input.parse()?, Box::new(unary(input)?));
        } else if input.peek(Punct!["%"]) {
            expr = Expr::Mod(Box::new(expr), input.parse()?, Box::new(unary(input)?));
        } else {
            break;
        }
    }
    Ok(expr)
}

fn unary(input: ParseStream) -> Result<Expr> {
    if input.peek(Punct!["-"]) {
        Ok(Expr::Neg(input.parse()?, Box::new(unary(input)?)))
    } else {
        primary(input)
    }
}
More examples
Hide additional examples
examples/lox/main.rs (line 195)
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    fn assignment(input: ParseStream) -> Result<Self> {
        let expr = Expr::or(input)?;

        if input.peek(Punct!["="]) {
            let equals: Punct!["="] = input.parse()?;
            let value = Box::new(Expr::assignment(input)?);

            if let Expr::Variable { name, .. } = expr {
                return Ok(Expr::Assign {
                    name,
                    value,
                    distance: Cell::new(None),
                });
            } else if let Expr::Get { object, name } = expr {
                return Ok(Expr::Set {
                    object,
                    name,
                    value,
                });
            }

            input.add_error(input.new_error(
                "Invalid assignment target".to_string(),
                &equals,
                error_codes::INVALID_ASSIGN,
            ));
        }

        Ok(expr)
    }

    fn or(input: ParseStream) -> Result<Self> {
        let mut expr = Expr::and(input)?;

        while input.peek(kw::or) {
            expr = Expr::Logical(Box::new(Logical::Or(
                expr,
                input.parse()?,
                Expr::and(input)?,
            )));
        }

        Ok(expr)
    }

    fn and(input: ParseStream) -> Result<Self> {
        let mut expr = Expr::equality(input)?;

        while input.peek(kw::and) {
            expr = Expr::Logical(Box::new(Logical::And(
                expr,
                input.parse()?,
                Expr::equality(input)?,
            )));
        }

        Ok(expr)
    }

    fn equality(input: ParseStream) -> Result<Self> {
        let mut expr = Expr::comparison(input)?;

        loop {
            if input.peek(Punct!["=="]) {
                expr = Expr::binary(Binary::Equal(
                    expr,
                    input.parse()?,
                    Expr::comparison(input)?,
                ));
            } else if input.peek(Punct!["!="]) {
                expr = Expr::binary(Binary::NotEqual(
                    expr,
                    input.parse()?,
                    Expr::comparison(input)?,
                ));
            } else {
                break Ok(expr);
            }
        }
    }

    fn comparison(input: ParseStream) -> Result<Self> {
        let mut expr = Expr::term(input)?;

        loop {
            if input.peek(Punct![">"]) {
                expr = Expr::binary(Binary::Greater(expr, input.parse()?, Expr::term(input)?));
            } else if input.peek(Punct![">="]) {
                expr = Expr::binary(Binary::GreaterEqual(
                    expr,
                    input.parse()?,
                    Expr::term(input)?,
                ));
            } else if input.peek(Punct!["<"]) {
                expr = Expr::binary(Binary::Less(expr, input.parse()?, Expr::term(input)?));
            } else if input.peek(Punct!["<="]) {
                expr = Expr::binary(Binary::LessEqual(expr, input.parse()?, Expr::term(input)?));
            } else {
                break Ok(expr);
            }
        }
    }

    fn term(input: ParseStream) -> Result<Self> {
        let mut expr = Expr::factor(input)?;

        loop {
            if input.peek(Punct!["+"]) {
                expr = Expr::binary(Binary::Add(expr, input.parse()?, Expr::factor(input)?));
            } else if input.peek(Punct!["-"]) {
                expr = Expr::binary(Binary::Sub(expr, input.parse()?, Expr::factor(input)?));
            } else {
                break Ok(expr);
            }
        }
    }

    fn factor(input: ParseStream) -> Result<Self> {
        let mut expr = Expr::unary(input)?;

        loop {
            if input.peek(Punct!["*"]) {
                expr = Expr::binary(Binary::Mul(expr, input.parse()?, Expr::unary(input)?));
            } else if input.peek(Punct!["/"]) {
                expr = Expr::binary(Binary::Div(expr, input.parse()?, Expr::unary(input)?));
            } else {
                break Ok(expr);
            }
        }
    }

    fn unary(input: ParseStream) -> Result<Self> {
        if input.peek(Punct!["-"]) {
            Ok(Expr::Unary(Box::new(Unary::Neg(
                input.parse()?,
                Expr::unary(input)?,
            ))))
        } else if input.peek(Punct!["!"]) {
            Ok(Expr::Unary(Box::new(Unary::Not(
                input.parse()?,
                Expr::unary(input)?,
            ))))
        } else {
            Expr::call(input)
        }
    }

    fn call(input: ParseStream) -> Result<Self> {
        let mut expr = Expr::primary(input)?;

        loop {
            if input.peek(Punct!["("]) {
                expr = Expr::finish_call(input, expr)?;
            } else if input.peek(Punct!["."]) {
                let _: Punct!["."] = input.parse()?;
                let name: Ident = input.parse()?;
                expr = Expr::Get {
                    object: Box::new(expr),
                    name,
                };
            } else {
                break Ok(expr);
            }
        }
    }

    fn finish_call(input: ParseStream<'_>, callee: Expr) -> Result<Self> {
        let content;
        let paren: Parentheses = group!(content in input);
        let arguments: Punctuated<Expr, Punct![","]> =
            Punctuated::parse_separated_trailing(&content)?;
        let arguments: Vec<_> = arguments.into_iter().collect();
        if arguments.len() >= 255 {
            input.add_error(input.new_error(
                "Can't have more than 254 arguments".to_string(),
                paren.0.clone(),
                error_codes::TOO_MANY_ARGS,
            ));
        }
        Ok(Expr::Call {
            callee: Box::new(callee),
            paren,
            arguments,
        })
    }

    fn primary(input: ParseStream) -> Result<Self> {
        let lookahead = input.lookahead();
        if lookahead.peek(kw::kw_false) {
            Ok(Expr::Literal(Literal::False(input.parse()?)))
        } else if lookahead.peek(kw::kw_true) {
            Ok(Expr::Literal(Literal::True(input.parse()?)))
        } else if lookahead.peek(kw::nil) {
            Ok(Expr::Literal(Literal::Nil(input.parse()?)))
        } else if lookahead.peek(LitFloat) {
            Ok(Expr::Literal(Literal::Float(input.parse()?)))
        } else if lookahead.peek(LitInt) {
            Ok(Expr::Literal(Literal::Int(input.parse()?)))
        } else if lookahead.peek(LitStr) {
            Ok(Expr::Literal(Literal::String(input.parse()?)))
        } else if input.peek(kw::kw_super) {
            Ok(Expr::Super {
                keyword: input.parse()?,
                distance: Cell::new(None),
                dot: input.parse()?,
                method: kw::ident(input)?,
            })
        } else if input.peek(kw::this) {
            Ok(Expr::This {
                keyword: input.parse()?,
                distance: Cell::new(None),
            })
        } else if lookahead.peek(Ident) {
            Ok(Expr::Variable {
                name: kw::ident(input)?,
                distance: Cell::new(None),
            })
        } else if lookahead.peek(Punct!["("]) {
            let content;
            let _: Parentheses = group!(content in input);
            Ok(Expr::Group(Box::new(content.parse()?)))
        } else {
            Err(lookahead.error())
        }
    }
}

impl Parse for Expr {
    fn parse(input: ParseStream) -> Result<Self> {
        Expr::assignment(input)
    }
}

#[derive(Debug, Clone, PartialEq)]
struct Function {
    name: Ident,
    params: Vec<Ident>,
    body: Vec<Stmt>,
}

impl Parse for Function {
    fn parse(input: ParseStream) -> Result<Self> {
        let name: Ident = input.parse()?;
        let mut contents: Group<Parentheses> = input.parse()?;
        contents.remove_whitespace();
        let Parentheses(span) = contents.delimiters();
        let tokens = contents.into_token_stream();
        let params: Vec<Ident> = if tokens.is_empty() {
            vec![]
        } else {
            let params: Punctuated<Ident, Punct![","]> =
                Punctuated::parse_separated.parse(tokens)?;
            params.into_iter().collect()
        };
        if params.len() >= 255 {
            input.add_error(input.new_error(
                "Can't have more than 254 parameters".to_string(),
                span,
                error_codes::TOO_MANY_ARGS,
            ));
        }
        let mut contents: Group<Braces> = input.parse()?;
        contents.remove_whitespace();
        let body = block.parse(contents.into_token_stream())?;
        Ok(Function { name, params, body })
    }
}

#[derive(Debug, Clone, PartialEq)]
enum Stmt {
    Block(Vec<Stmt>),
    Class {
        name: Ident,
        superclass: Option<Ident>,
        superclass_distance: Cell<Option<usize>>,
        methods: Vec<Function>,
    },
    Expr(Expr),
    Function(Function),
    If {
        condition: Expr,
        then_branch: Box<Stmt>,
        else_branch: Option<Box<Stmt>>,
    },
    Print(Expr),
    Return {
        keyword: kw::kw_return,
        value: Option<Expr>,
    },
    Variable {
        name: Ident,
        initialiser: Option<Expr>,
    },
    While {
        condition: Expr,
        body: Box<Stmt>,
    },
}

fn block(input: ParseStream) -> Result<Vec<Stmt>> {
    let mut statements = vec![];

    while !input.is_empty() {
        statements.push(Stmt::declaration(input)?);
    }

    Ok(statements)
}

impl Stmt {
    fn declaration(input: ParseStream) -> Result<Self> {
        if input.peek(kw::class) {
            Stmt::class_declaration(input)
        } else if input.peek(kw::fun) {
            let _: kw::fun = input.parse()?;
            Ok(Stmt::Function(Function::parse(input)?))
        } else if input.peek(kw::var) {
            Stmt::var_declaration(input)
        } else {
            Stmt::statement(input)
        }
    }

    fn class_declaration(input: ParseStream) -> Result<Self> {
        let _: kw::class = input.parse()?;
        let name: Ident = input.parse()?;

        let superclass = if input.peek(Punct!["<"]) {
            let _: Punct!["<"] = input.parse()?;
            Some(input.parse()?)
        } else {
            None
        };

        let content;
        let _: Braces = group!(content in input);
        let methods = parse_repeated(&content)?;

        Ok(Stmt::Class {
            name,
            superclass,
            superclass_distance: Cell::new(None),
            methods,
        })
    }

    fn var_declaration(input: ParseStream) -> Result<Self> {
        let _: kw::var = input.parse()?;

        let name = kw::ident(input)?;

        let initialiser = if input.peek(Punct!["="]) {
            let _: Punct!["="] = input.parse()?;
            Some(input.parse()?)
        } else {
            None
        };

        let _: Punct![";"] = input.parse()?;
        Ok(Stmt::Variable { name, initialiser })
    }

    fn statement(input: ParseStream) -> Result<Self> {
        if input.peek(kw::kw_if) {
            Stmt::if_statement(input)
        } else if input.peek(kw::kw_for) {
            Stmt::for_statement(input)
        } else if input.peek(kw::print) {
            Stmt::print_statement(input)
        } else if input.peek(kw::kw_return) {
            Stmt::return_statement(input)
        } else if input.peek(kw::kw_while) {
            Stmt::while_statement(input)
        } else if input.peek(Punct!["{"]) {
            let content;
            let _: Braces = group!(content in input);
            Ok(Stmt::Block(block(&content)?))
        } else {
            Stmt::expression_statement(input)
        }
    }

    fn for_statement(input: ParseStream) -> Result<Self> {
        let _: kw::kw_for = input.parse()?;

        let content;
        let _: Parentheses = group!(content in input);

        let initialiser = if content.peek(Punct![";"]) {
            let _: Punct![";"] = content.parse()?;
            None
        } else if content.peek(kw::var) {
            Some(Stmt::var_declaration(&content)?)
        } else {
            Some(Stmt::expression_statement(&content)?)
        };

        let condition = if content.peek(Punct![";"]) {
            Expr::Literal(Literal::True(kw::kw_true::new(&content)))
        } else {
            content.parse()?
        };
        let _: Punct![";"] = content.parse()?;

        let increment = if content.is_empty() {
            None
        } else {
            Some(content.parse()?)
        };

        let mut body = Stmt::statement(input)?;

        if let Some(increment) = increment {
            body = Stmt::Block(vec![body, Stmt::Expr(increment)]);
        }

        body = Stmt::While {
            condition,
            body: Box::new(body),
        };

        if let Some(initialiser) = initialiser {
            body = Stmt::Block(vec![initialiser, body]);
        }

        Ok(body)
    }

    fn if_statement(input: ParseStream) -> Result<Self> {
        let _: kw::kw_if = input.parse()?;
        let content;
        let _: Parentheses = group!(content in input);
        let condition = content.parse()?;

        let then_branch = Box::new(Stmt::statement(input)?);
        let else_branch = if input.peek(kw::kw_else) {
            Some(Box::new(Stmt::statement(input)?))
        } else {
            None
        };

        Ok(Stmt::If {
            condition,
            then_branch,
            else_branch,
        })
    }

    fn print_statement(input: ParseStream) -> Result<Self> {
        let _: kw::print = input.parse()?;
        let value = input.parse()?;
        let _: Punct![";"] = input.parse()?;
        Ok(Self::Print(value))
    }

    fn return_statement(input: ParseStream) -> Result<Self> {
        let keyword: kw::kw_return = input.parse()?;
        let value = if input.peek(Punct![";"]) {
            None
        } else {
            Some(input.parse()?)
        };
        let _: Punct![";"] = input.parse()?;
        Ok(Stmt::Return { keyword, value })
    }

    fn while_statement(input: ParseStream) -> Result<Self> {
        let _: kw::kw_while = input.parse()?;
        let content;
        let _: Parentheses = group!(content in input);
        let condition = content.parse()?;
        let body = Box::new(Stmt::statement(input)?);

        Ok(Stmt::While { condition, body })
    }

    fn expression_statement(input: ParseStream) -> Result<Self> {
        let expr = input.parse()?;
        let _: Punct![";"] = input.parse()?;
        Ok(Self::Expr(expr))
    }
}

impl Parse for Stmt {
    fn parse(input: ParseStream) -> Result<Self> {
        Stmt::declaration(input)
    }
}

struct Ast(Vec<Stmt>);

impl Ast {
    #[allow(clippy::wildcard_imports)]
    fn synchronise(input: ParseStream) {
        input.synchronise(|input| {
            use kw::*;
            input.peek(Punct![";"]) && !input.peek2(Punct!["}"])
                || peek2_any!(input, class, kw_for, fun, kw_if, print, kw_return, var, kw_while)
        });
    }
source

pub fn peek2<T: Peek>(&self, token: T) -> bool

Returns true if the next token is an instance of T.

Note that for the purposes of this function, multi-character punctuation like += is considered to be two tokens, and float literals are considered to be three tokens (start, ., end).

Examples found in repository?
examples/lox/main.rs (line 688)
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    fn synchronise(input: ParseStream) {
        input.synchronise(|input| {
            use kw::*;
            input.peek(Punct![";"]) && !input.peek2(Punct!["}"])
                || peek2_any!(input, class, kw_for, fun, kw_if, print, kw_return, var, kw_while)
        });
    }
source

pub fn current_span(&self) -> Result<Span>

Gets the span of the current token.

Errors

Returns an error if self is empty.

source

pub fn fork(&self) -> ParseBuffer<'a>

Creates a new ParseBuffer at the same position as self.

Changes to self will not affect the fork, and vice versa.

source

pub fn commit(&self, fork: &Self)

Commits a forked buffer into self, updating self to reflect fork.

Panics

This function will panic if fork wasn’t forked from self or if self is further ahead than fork.

source

pub fn unexpected_token(&self, expected: HashSet<String>) -> Error

Creates an error with the message Unexpected token and the given expected tokens.

Use of this function is generally discouraged in favour of Lookahead::error.

source

pub fn lookahead(&self) -> Lookahead<'a>

Creates a helper struct for peeking at the next token.

Examples found in repository?
examples/calc.rs (line 82)
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fn primary(input: ParseStream) -> Result<Expr> {
    let lookahead = input.lookahead();
    if lookahead.peek(token::LitFloat) {
        Ok(Expr::Num(input.parse::<token::LitFloat>()?.value()))
    } else if lookahead.peek(token::LitInt) {
        Ok(Expr::Num(input.parse::<token::LitInt>()?.value() as f64))
    } else if lookahead.peek(token::LeftParen) {
        let group: Group<Parentheses> = input.parse()?;
        parse(group.into_token_stream())
    } else {
        Err(lookahead.error())
    }
}
More examples
Hide additional examples
examples/lox/main.rs (line 379)
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    fn primary(input: ParseStream) -> Result<Self> {
        let lookahead = input.lookahead();
        if lookahead.peek(kw::kw_false) {
            Ok(Expr::Literal(Literal::False(input.parse()?)))
        } else if lookahead.peek(kw::kw_true) {
            Ok(Expr::Literal(Literal::True(input.parse()?)))
        } else if lookahead.peek(kw::nil) {
            Ok(Expr::Literal(Literal::Nil(input.parse()?)))
        } else if lookahead.peek(LitFloat) {
            Ok(Expr::Literal(Literal::Float(input.parse()?)))
        } else if lookahead.peek(LitInt) {
            Ok(Expr::Literal(Literal::Int(input.parse()?)))
        } else if lookahead.peek(LitStr) {
            Ok(Expr::Literal(Literal::String(input.parse()?)))
        } else if input.peek(kw::kw_super) {
            Ok(Expr::Super {
                keyword: input.parse()?,
                distance: Cell::new(None),
                dot: input.parse()?,
                method: kw::ident(input)?,
            })
        } else if input.peek(kw::this) {
            Ok(Expr::This {
                keyword: input.parse()?,
                distance: Cell::new(None),
            })
        } else if lookahead.peek(Ident) {
            Ok(Expr::Variable {
                name: kw::ident(input)?,
                distance: Cell::new(None),
            })
        } else if lookahead.peek(Punct!["("]) {
            let content;
            let _: Parentheses = group!(content in input);
            Ok(Expr::Group(Box::new(content.parse()?)))
        } else {
            Err(lookahead.error())
        }
    }
source

pub fn skip_whitespace(&self)

Skips over all whitespace tokens before the next non-whitespace token.

This method will not skip newlines.

source

pub fn empty_span(&self) -> Span

Creates a new empty Span with this stream’s source file.

Trait Implementations§

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impl Debug for ParseBuffer<'_>

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fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
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impl<'a> From<&'a TokenStream> for ParseBuffer<'a>

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fn from(value: &'a TokenStream) -> Self

Converts to this type from the input type.
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impl<'a> From<TokenStream> for ParseBuffer<'a>

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fn from(value: TokenStream) -> Self

Converts to this type from the input type.

Auto Trait Implementations§

§

impl<'a> RefUnwindSafe for ParseBuffer<'a>

§

impl<'a> Send for ParseBuffer<'a>

§

impl<'a> Sync for ParseBuffer<'a>

§

impl<'a> Unpin for ParseBuffer<'a>

§

impl<'a> UnwindSafe for ParseBuffer<'a>

Blanket Implementations§

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impl<T> Any for T
where T: 'static + ?Sized,

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fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more
source§

impl<T> Borrow<T> for T
where T: ?Sized,

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fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
source§

impl<T> BorrowMut<T> for T
where T: ?Sized,

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fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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impl<T> From<T> for T

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fn from(t: T) -> T

Returns the argument unchanged.

source§

impl<T, U> Into<U> for T
where U: From<T>,

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fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

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impl<T, U> TryFrom<U> for T
where U: Into<T>,

§

type Error = Infallible

The type returned in the event of a conversion error.
source§

fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

§

type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
source§

fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.