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Add a new
ParserExtra::State: Inspector trait
This allows using imperative concrete syntax tree parsers like `rowan` and `cstree`.
In particular those libraries want to know every token that is parsed, and need to know when chumsky backtracks and reparses the same tokens again.
This adds the following new API surface:
```rust
pub trait Inspector<'a, I: Input<'a>>: Default {
type SaveMarker: Copy + Clone;
fn on_token(&mut self, token: &I::Token);
fn on_save<'parse>(&self, offset: I::Offset) -> Self::SaveMarker;
fn on_rewind<'parse>(&mut self, marker: Marker<'a, 'parse, I, Self::SaveMarker>);
}
pub struct SimpleState<T>(pub T);
impl<'a, T, I: Input<'a>> Inspector<'a, I> for SimpleState<T>;
impl<T> DerefMut<Target = T> for SimpleState<T>;
impl<T> From<T> for SimpleState<T>;
```
and additionally now requires `ParserExtra::State: Inspector`.- Loading branch information
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,70 @@ | ||
| //! Parser extensions that inspect the input without modifying it. | ||
| //! | ||
| //! *"Only one man stood and watched the sky, stood with terrible sadness in his eyes | ||
| //! and rubber bungs in his ears. He knew exactly what was happening and had known | ||
| //! ever since his Sub-Etha Sens-O-Matic had started winking in the dead of night | ||
| //! beside his pillar and woken him with a start."* | ||
| use crate::{input::Marker, Input}; | ||
| use core::ops::{Deref, DerefMut}; | ||
|
|
||
| #[allow(unused)] // for intra-doc links | ||
| use crate::Parser; | ||
|
|
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| /// A type that receives event hooks when certain parsing actions occur. | ||
| /// | ||
| /// If you don't need to receive event hooks, use [`SimpleState`]. | ||
| pub trait Inspector<'a, I: Input<'a>> { | ||
| /// A type the Recorder can use to revert to a previous state. | ||
| /// | ||
| /// For implementation reasons, this is required to be `Copy + Clone`. | ||
| type SaveMarker: Copy + Clone; | ||
|
|
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| /// This function is called when a new token is read from the input stream. | ||
| // impl note: this should be called only when `self.offset` is updated, not when we only peek at the next token. | ||
| fn on_token(&mut self, token: &I::Token); | ||
| /// This function is called when a combinator saves the current state of the parse. | ||
| fn on_save<'parse>(&self, offset: I::Offset) -> Self::SaveMarker; | ||
| /// This function is called when a combinator rewinds to an earlier state of the parser. | ||
| /// | ||
| /// You can use [`Marker::ext_marker`] to get back the [`SaveMarker`][Self::SaveMarker] | ||
| /// you originally created in [`on_save`][Self::on_save]. | ||
| fn on_rewind<'parse>(&mut self, marker: Marker<'a, 'parse, I, Self::SaveMarker>); | ||
| } | ||
|
|
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| impl<'a, I: Input<'a>> Inspector<'a, I> for () { | ||
| type SaveMarker = (); | ||
| fn on_token(&mut self, _: &<I as Input<'a>>::Token) {} | ||
| fn on_save<'parse>(&self, _: <I as Input<'a>>::Offset) -> Self::SaveMarker {} | ||
| fn on_rewind<'parse>(&mut self, _: Marker<'a, 'parse, I, Self>) {} | ||
| } | ||
|
|
||
| /// A state type that should be accessible directly from `parser.state()` and has no special behavior. | ||
| /// | ||
| /// This wrapper implements the [`Recorder`] trait for you so you don't have to. | ||
| pub struct SimpleState<T>(pub T); | ||
| impl<'a, T, I: Input<'a>> Inspector<'a, I> for SimpleState<T> { | ||
| type SaveMarker = (); | ||
| fn on_token(&mut self, _: &<I as Input<'a>>::Token) {} | ||
| fn on_save<'parse>(&self, _: <I as Input<'a>>::Offset) -> Self::SaveMarker {} | ||
| fn on_rewind<'parse>(&mut self, _: Marker<'a, 'parse, I, Self::SaveMarker>) {} | ||
| } | ||
|
|
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| impl<T> Deref for SimpleState<T> { | ||
| type Target = T; | ||
|
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| fn deref(&self) -> &Self::Target { | ||
| &self.0 | ||
| } | ||
| } | ||
|
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| impl<T> DerefMut for SimpleState<T> { | ||
| fn deref_mut(&mut self) -> &mut Self::Target { | ||
| &mut self.0 | ||
| } | ||
| } | ||
|
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| impl<T> From<T> for SimpleState<T> { | ||
| fn from(value: T) -> Self { | ||
| Self(value) | ||
| } | ||
| } |