libspecr 0.1.41

standard library for specr lang
Documentation 
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use std::ops::*;

/// Extension trait to implement `try_map` on Options.
pub trait OptionExt<T> {
    /// applies the fallible function `f` to the inner value of `self` and transposes the result.
    /// Given `f: T -> Result<O, Err>`
    /// we have `try_map(f): Option<T> -> Result<Option<O>, Err>`
    fn try_map<O, E>(self, f: impl FnOnce(T) -> E) -> <<E as Try>::Residual as Residual<Option<O>>>::TryType
        where E: Try<Output=O>,
              <E as Try>::Residual: Residual<Option<O>>;
}

impl<T> OptionExt<T> for Option<T> {
    fn try_map<O, E>(self, f: impl FnOnce(T) -> E) -> <<E as Try>::Residual as Residual<Option<O>>>::TryType
        where E: Try<Output=O>,
              <E as Try>::Residual: Residual<Option<O>>
    {
        <<<E as Try>::Residual as Residual<Option<O>>>::TryType>::from_output(match self {
            Some(x) => Some(f(x)?),
            None => None,
        })
    }
}

#[test]
fn option_ext_test() {
    use crate::*;

    struct In;
    struct Out;
    struct Error;

    let ok: fn(In) -> NdResult<Out, Error> = |_: In| NdResult(Ok(Out));
    let err: fn(In) -> NdResult<Out, Error> = |_: In| NdResult(Err(Error));

    assert!(matches!(
        Some(In).try_map(ok),
        NdResult(Ok(Some(Out)))
    ));
    assert!(matches!(
        None.try_map(ok),
        NdResult(Ok(None))
    ));
    assert!(matches!(
        Some(In).try_map(err),
        NdResult(Err(Error))
    ));
    assert!(matches!(
        None.try_map(err),
        NdResult(Ok(None))
    ));
}