lalrpop/doc/calculator/src/calculator6.lalrpop

use std::str::FromStr;
use ast::{Expr, Opcode};
use lalrpop_util::ErrorRecovery;

grammar<'err>(errors: &'err mut Vec<ErrorRecovery<usize, (usize, &'input str), ()>>);

pub Exprs = Comma<Expr>;

Comma<T>: Vec<T> = { // (0)
    <v:(<T> ",")*> <e:T?> => match e { // (1)
        None=> v,
        Some(e) => {
            let mut v = v;
            v.push(e);
            v
        }
    }
};

Tier<Op,NextTier>: Box<Expr> = {
    Tier<Op,NextTier> Op NextTier => Box::new(Expr::Op(<>)),
    NextTier
};

Expr = Tier<ExprOp, Factor>;
Factor = Tier<FactorOp, Term>;

ExprOp: Opcode = { // (3)
    "+" => Opcode::Add,
    "-" => Opcode::Sub,
};

FactorOp: Opcode = {
    "*" => Opcode::Mul,
    "/" => Opcode::Div,
};

Term: Box<Expr> = {
    Num => Box::new(Expr::Number(<>)),
    "(" <Expr> ")",
    ! => { errors.push(<>); Box::new(Expr::Error) },
};

Num: i32 = {
    r"[0-9]+" => i32::from_str(<>).unwrap()
};