feat(pc): Introducing err_supplier

Author: ngeor

rusty_parser/src/core/var_name.rs

@@ -190,7 +190,7 @@ fn bare<T>()
 where
     T: Default + VarType,
 {
-    supplier::supplier(|| T::default())
+    supplier(T::default)
 }
 
 fn name_with_opt_array<P>(

rusty_pc/src/lib.rs

@@ -20,7 +20,7 @@ pub mod or_default;
 mod parser;
 pub mod peek;
 mod seq;
-pub mod supplier;
+mod supplier;
 mod surround;
 pub mod text;
 mod then_with;
@@ -35,6 +35,7 @@ pub use lazy::*;
 pub use or::*;
 pub use parser::*;
 pub use seq::*;
+pub use supplier::*;
 pub use surround::*;
 pub use then_with::*;
 pub use then_with_left::*;

rusty_pc/src/supplier.rs

@@ -2,6 +2,7 @@ use std::marker::PhantomData;
 
 use crate::{InputTrait, Parser, ParserErrorTrait, SetContext};
 
+/// A parser that always succeeds, providing the value returned by the given function.
 pub fn supplier<I, C, F, O, E>(f: F) -> impl Parser<I, C, Output = O, Error = E> + SetContext<C>
 where
     I: InputTrait,
@@ -27,6 +28,36 @@ where
     }
 }
 
-impl<C, P, F> SetContext<C> for SupplierParser<P, F> {
+impl<C, F, E> SetContext<C> for SupplierParser<F, E> {
+    fn set_context(&mut self, _ctx: C) {}
+}
+
+/// A parser that always fails, providing the value returned by the given function.
+pub fn err_supplier<I, C, F, O, E>(f: F) -> impl Parser<I, C, Output = O, Error = E> + SetContext<C>
+where
+    I: InputTrait,
+    F: Fn() -> E,
+    E: ParserErrorTrait,
+{
+    ErrSupplierParser(f, PhantomData)
+}
+
+struct ErrSupplierParser<F, O>(F, PhantomData<O>);
+
+impl<I, C, F, O, E> Parser<I, C> for ErrSupplierParser<F, O>
+where
+    I: InputTrait,
+    F: Fn() -> E,
+    E: ParserErrorTrait,
+{
+    type Output = O;
+    type Error = E;
+
+    fn parse(&mut self, _input: &mut I) -> Result<O, E> {
+        Err((self.0)())
+    }
+}
+
+impl<C, F, O> SetContext<C> for ErrSupplierParser<F, O> {
     fn set_context(&mut self, _ctx: C) {}
 }