Trial a Rust engine powering a Civet interface

Write a basic web app with a Rust engine, compiled to WebAssembly,
powering a Civet interface. Do linear algebra in the engine using
the `nalgebra` crate.

lang-trials/rust/src/lib.rs

@@ -0,0 +1,55 @@
+mod utils;
+
+extern crate js_sys;
+
+use nalgebra::*;
+use wasm_bindgen::prelude::*;
+
+#[wasm_bindgen]
+pub struct Circle {
+    pub center_x: f64,
+    pub center_y: f64,
+    pub radius: f64,
+}
+
+// construct the circle through
+//
+//   (x1, y1), (x2, y2), (x3, y3)
+//
+// from the array
+//
+//   [x1, y1, x2, y2, x3, y3]
+//
+#[wasm_bindgen]
+pub fn circThru(data_raw: js_sys::Float64Array) -> Result<Circle, JsValue> {
+    // represent the given points as the columns of a matrix
+    let data = Matrix2x3::from_vec(data_raw.to_vec());
+    
+    // build the matrix that maps the circle's coefficient vector to the
+    // negative of the linear part of the circle's equation, evaluated at the
+    // given points
+    let neg_lin_part = stack![2.0*data.transpose(), Vector3::repeat(1.0)];
+    
+    // find the quadrdatic part of the circle's equation, evaluated at the given
+    // points
+    let quad_part = Vector3::from_iterator(
+        data.column_iter().map(|v| v.dot(&v))
+    );
+    
+    // find the circle's coefficient vector, and from there its center and
+    // radius
+    match neg_lin_part.lu().solve(&quad_part) {
+        None => Err(JsValue::from("Couldn't solve system")),
+        Some(coeffs) => {
+            let center_x = coeffs[0];
+            let center_y = coeffs[1];
+            Ok(Circle {
+                center_x: center_x,
+                center_y: center_y,
+                radius: (
+                    coeffs[2] + center_x*center_x + center_y*center_y
+                ).sqrt(),
+            })
+        }
+    }
+}

lang-trials/rust/src/utils.rs

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+pub fn set_panic_hook() {
+    // When the `console_error_panic_hook` feature is enabled, we can call the
+    // `set_panic_hook` function at least once during initialization, and then
+    // we will get better error messages if our code ever panics.
+    //
+    // For more details see
+    // https://github.com/rustwasm/console_error_panic_hook#readme
+    #[cfg(feature = "console_error_panic_hook")]
+    console_error_panic_hook::set_once();
+}