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//! This file defines the expected behaviours of a recursive descent
//! parser.
use super::Regex;
use graph::GraphLabel;
/// A thin wrapper of the parse output, to simplify the function
/// signature a little.
pub type ParseOutput<'a, T> = Option<(T, &'a str)>;
/// Types implementing this trait provide a method to be recursively
/// parsed.
pub trait DesRec {
/// The type of labels of the resulting regular expression.
type Label: GraphLabel;
/// The type of the resulting regular expression.
type Regex: Regex<Self::Label>;
/// The type of errors encountered when parsing.
type Error: std::error::Error;
/// Auxiliary data when parsing
type Aux;
/// The type of a scanner that classifies inputs into tokens.
///
/// The return type indicates the result of classification:
///
/// - `Err(_)`: the classification fails
///
/// - `Ok(None)`: the classification succeeds, and the parsing
/// should stop here
///
/// - `Ok(Some(_))`: the classification succeeds and the parsing
/// should continue.
type Scanner<'a>: FnMut(&'a str) -> Result<Option<(usize, Self::Label, Self::Aux)>, Self::Error>;
/// Parse a string into a regular expression with the aid of this
/// type.
///
/// Accept a slice of string and return either a parsing error, or
/// a pair of correctly parsed regular expression and the
/// remaining slice.
fn parse<'a>(
input: &'a str,
scanner: Self::Scanner<'a>,
post_p: bool,
) -> Result<ParseOutput<'a, Self::Regex>, Self::Error>;
}
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