Type Alias Function 

pub type Function = dyn for<'a> Fn(&Value<'a>) -> Value<'a> + Send + Sync;

Alias for a trait object that represents a function that can be called from Dent. The function takes a reference to a value and returns a value.

The function can be called from Dent using the @ operator, after being registered with Dent::add_function.

A Dent function can only take a single argument, for simplicity. If you need to pass multiple arguments, you can use a list or dictionary.

Examples

use dent_parse::{Dent, Value, Function};
use std::collections::HashMap;

let mut functions: HashMap<String, Box<Function>> = HashMap::new();
functions.insert(
    "sum".to_string(),
    Box::new(move |value: &Value| -> Value {
        let mut sum = 0;
        if let Value::List(values) = value {
            for value in values.iter() {
                if let Value::Int(i) = value {
                    sum += i;
                }
            }
            Value::Int(sum)
        } else if let Value::Int(i) = value {
            Value::Int(*i)
        } else {
            Value::None
        }
    }),
);
let parser = Dent::new(functions);

assert_eq!(parser.parse("@sum {}"), Ok(Value::None));
assert_eq!(parser.parse("@sum 0"), Ok(Value::Int(0)));
assert_eq!(parser.parse("@sum [ 1 2 3 ]"), Ok(Value::Int(6)));