rust_dynamic 0.49.0

use crate::value::{Value};

pub type CtxAppFn  = fn(&dyn Context,&str,Value) -> Option<Value>;

//
// Number of required operands for the Applicatives
//
pub const NOEXTRA: u16         = 0;
pub const JUSTONE: u16         = 1;
pub const JUSTTWO: u16         = 2;
pub const TAKEALL: u16         = 3;


#[derive(Clone)]
pub struct CtxApplicative {
    pub name:   String,
    pub extra:  u16,
    pub f:      CtxAppFn,
}

impl CtxApplicative {
    pub fn new<N: AsRef<str> + std::fmt::Display>(name: N, e: u16, f: CtxAppFn) -> Self {
        Self {
            name:   name.as_ref().to_string(),
            extra:  e,
            f:      f,
        }
    }
}


pub trait Context {
    fn new() -> Self where Self: Sized;
    fn resolve(&self, name: &str) -> Option<CtxApplicative>;
    fn get_association(&self, name: &str) -> Option<Value>;
    fn register(&mut self, name: &str, f: CtxApplicative) -> bool;
    fn register_association(&mut self, name: &str, v: Value) -> bool;
    fn eval(&mut self, a: Option<CtxApplicative>, v: Value) -> Option<Value>;
}

pub struct NullContext {}

impl Context for NullContext {
    fn new() -> NullContext {
        Self {

        }
    }
    fn resolve(&self, _name: &str) -> Option<CtxApplicative> {
        fn none_fn(_ctx: &dyn Context, _name: &str, _value: Value) -> Option<Value> {
            None
        }
        Some(CtxApplicative::new("none_fn", NOEXTRA, none_fn))
    }
    fn get_association(&self, _name: &str) -> Option<Value> {
        None
    }
    fn register(&mut self, _name: &str, _f: CtxApplicative) -> bool {
        true
    }
    fn register_association(&mut self, _name: &str, _v: Value) -> bool {
        true
    }
    fn eval(&mut self, _a: Option<CtxApplicative>, _v: Value) -> Option<Value> {
        None
    }
}


pub fn context(mut ctx: impl Context, value: Value) -> Option<Value> {
    ctx.eval(None, value)
}