tengri/dsl/src/dsl_provide.rs

use crate::*;

/// Map EDN tokens to parameters of a given type for a given context
/// TODO: Replace both [Context] and [TryFromDsl] with this trait
/// which returns a [Result].
pub trait Dsl<U>: Sized {
    fn take <'state, 'source> (_: &'state Self, _: &mut TokenIter<'source>) -> Perhaps<U> {
        Ok(None)
    }
    fn take_or_fail <'state, 'source> (
        state: &'state Self, iter: &mut TokenIter<'source>
    ) -> Usually<U> {
        if let Some(value) = Self::take(state, iter)? {
            Ok(value)
        } else {
            Result::Err("not found".into()) // TODO add info and error type
        }
    }
}

/// Map EDN tokens to parameters of a given type for a given context
pub trait Context<'state, U>: Sized {
    fn get <'source> (&'state self, _iter: &mut TokenIter<'source>) -> Option<U> {
        None
    }
}

impl<'state, T: Context<'state, U>, U> Context<'state, U> for &T {
    fn get <'source> (&'state self, iter: &mut TokenIter<'source>) -> Option<U> {
        (*self).get(iter)
    }
}

impl<'state, T: Context<'state, U>, U> Context<'state, U> for Option<T> {
    fn get <'source> (&'state self, iter: &mut TokenIter<'source>) -> Option<U> {
        self.as_ref().map(|s|s.get(iter)).flatten()
    }
}

pub trait TryFromDsl<'state, T>: Sized {
    fn try_from_expr <'source: 'state> (
        _state: &'state T, _iter: &mut TokenIter<'source>
    ) -> Option<Self> {
        None
    }
    fn try_from_atom <'source: 'state> (
        state: &'state T, value: Value<'source>
    ) -> Option<Self> {
        if let Exp(0, mut iter) = value {
            return Self::try_from_expr(state, &mut iter)
        }
        None
    }
}