Struct rcombinators::combinators::Lazy

pub struct Lazy<P, F: FnMut() -> P>(_, _);

Lazy is a helper for a typical situation where you have an Alternative or a Sequence and don't want to construct an expensive parser every time just in order for it to be dropped without having parsed anything. For example:

// Let's say dict is really expensive! the first ones not as much
let mut p = Alternative::new((number(), string(), atom(), dict()));

Then you can wrap the dict parser constructor in a Lazy parser. Then it will only be constructed if the Alternative actually needs a dict parser:

let mut p = Alternative::new((number(), string(), atom(), Lazy::new(dict)));

Constructing a Lazy combinator is in comparison quite cheap, as it only involves copying a function pointer. Lazy also caches the result of the function, meaning it will be called at most once.

Methods

impl<R, P: Parser<Result = R>, F: FnMut() -> P> Lazy<P, F>

pub fn new(f: F) -> Lazy<P, F>

Create a new instance of Lazy:

let l = Lazy::new(|| some_expensive_function());

Trait Implementations

impl<R, P: Parser<Result = R>, F: FnMut() -> P> Parser for Lazy<P, F>

type Result = R

fn parse(
    &mut self,
    st: &mut ParseState<impl Iterator<Item = char>>
) -> ParseResult<Self::Result>

parse consumes input from st and returns a result or an error.

fn apply<R2, F: Fn(Self::Result) -> ParseResult<R2>>(
    self,
    f: F
) -> Transform<Self::Result, R2, Self, F> where
    Self: Sized, 

apply transforms the result of this parser using a Transform combinator.

fn then<R2, P: Parser<Result = R2>>(self, p: P) -> Then<Self, P> where
    Self: Sized, 

then attempts to parse input, and if it succeeds, executes parser p, only returning p's result. This is useful for chaining parsers of which the results are not need.