This library is used to define types that implement the trait FiniteElement

The types are defined by procedural macros. To create a new type, one must first define an unit-like Structure and implement the trait AutoImplementable for it. Once the trait AutoImplementable has been implemented it is possible to define a proc macro that will generate the deffinition of a new type and an implementation of the trait FiniteElement for it.

Creation of a new macro

To create a new macro, one must first define a Zero-Sized struct, and implement the trait AutoImplementable for it. For example if we want to create an element representing a spring, we first create a zero-sized struct: pub struct _Spring{} and the implement the trait Autotimplementable for it.

The types that implement the trait AutoImplementable can be passed as type argument to the function macro_def<F: Float, T: AutoImplementable<F>>() -> TokenStream. This function can be used to define a procedural macro that will generate the code defining the corresponding structure and its implementation of the trait FiniteElement. Complete example (copied-pasted from spring.rs)

use crate::formal::{Formal, FormalVector, FormalPoint, Float};
use crate::autoimplementable::AutoImplementable;

use std::collections::HashMap;

// A `Spring` likes it when `a` and `b` are at distance `l`, and
// exerts a force of `k.(|ab| - l)` to achieve this.
pub struct _Spring{}

impl<F: Float> AutoImplementable<F> for _Spring {
   fn struct_name() -> String {
       String::from("Spring")
   }

   fn elt_list() -> Vec<String> {
       vec![String::from("a"), String::from("b")]
   }

   fn cst_list() -> Vec<String> {
       vec![String::from("l"), String::from("k")]
   }

   fn formal_map() -> HashMap<String, FormalVector<F>> {
   //Create a `Formal` for each element coordiate and each constants
       let point_a = FormalPoint {
           x: Formal::new_var(0),
           y: Formal::new_var(1),
           z: Formal::new_var(2)
       };

       let point_b = FormalPoint {
           x: Formal::new_var(3),
           y: Formal::new_var(4),
           z: Formal::new_var(5)
       };

       let cst_l = Formal::new_var(6);
       let cst_k = Formal::new_var(7);

       // The force applied on point a is k(|ab| - l) * ab/|ab|
       let ab = point_b - point_a;
       let force_a: FormalVector<F> = (ab.clone().norm() - cst_l.clone()) * ab.clone()/ab.clone().norm() * cst_k.clone();

       // The force applied on point b is k(|ba| - l) * ba/|ba|
       let force_b = (ab.clone().norm() - cst_l.clone()) * ab.clone()/ab.clone().norm() * cst_k.clone() * Formal::new_cst(F::one().neg());
       let mut ret = HashMap::new();
       ret.insert(String::from("a"), force_a);
       ret.insert(String::from("b"), force_b);
       ret
   }

}

// Once the trait is implemented, we can write a procedural macro
#[proc_macro]
pub fn auto_impl_spring(_item: TokenStream) -> TokenStream {
   macro_def::<f32, _Spring>()
}