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## adding_twice
### Instructions
In this exercise you will have to reuse your `add_curry` function (copy and paste it directly in your lib.rs file).
Then you have to create the function `twice` using closures, this function will
take a function f(x) as parameter and return a function f(f(x)).
So, the purpose of this function is to add two times the value in `add_curry` to the original value.
### Notions
- [higher order function](https://doc.rust-lang.org/rust-by-example/fn/hof.html#higher-order-functions)
### Expected functions
The type of the arguments are missing. Use the example `main` function to determine the correct type.
```rust
pub fn twice<T>(F: _) -> _{
}
```
### Usage
Here is a program to test your function.
```rust
use adding_twice::*;
fn main() {
let add10 = add_curry(10);
let value = twice(add10);
println!("The value is {}", value(7));
let add20 = add_curry(20);
let value = twice(add20);
println!("The value is {}", value(7));
let add30 = add_curry(30);
let value = twice(add30);
println!("The value is {}", value(7));
let neg = add_curry(-32);
let value = twice(neg);
println!("The value is {}", value(7));
}
```
And its output
```console
$ cargo run
The value is 27
The value is 47
The value is 67
The value is -57
$
```