knitr-engine.md
In rextendr: Call Rust Code from R using the 'extendr' Crate

Snapshot test of knitr-engine

Code
  cat_file(output)
Output



  Basic use example:


  ```r
  library(rextendr)

  # create a Rust function
  rust_function("fn add(a:f64, b:f64) -> f64 { a + b }")

  # call it from R
  add(2.5, 4.7)
  #> [1] 7.2
  ```

  The package also enables a new chunk type for knitr, `extendr`, which compiles and evaluates Rust code. For example, a code chunk such as this one:
  ````markdown
  ```{extendr}
  rprintln!("Hello from Rust!");

  let x = 5;
  let y = 7;
  let z = x*y;

  z
  ```
  ````

  would create the following output in the knitted document:

  ```rust
  rprintln!("Hello from Rust!");

  let x = 5;
  let y = 7;
  let z = x*y;

  z
  #> Hello from Rust!
  #> [1] 35
  ```

  Define variable `_x`:


  ```rust
  let _x = 1;
  ```

  Define variable `_y`:


  ```rust
  let _y = 2;
  ```

  Print:


  ```rust
  rprintln!("x = {}, y = {}", _x, _y);
  #> x = 1, y = 2
  ```


  ```rust
  use pulldown_cmark::{Parser, Options, html};

  #[extendr]
  fn md_to_html(input: &str) -> String {
      let mut options = Options::empty();
      options.insert(Options::ENABLE_TABLES);
      let parser = Parser::new_ext(input, options);
      let mut output = String::new();
      html::push_html(&mut output, parser);
      output
  }
  ```


  ```r
  md_text <- "# The story of the fox
  The quick brown fox **jumps over** the lazy dog.
  The quick *brown fox* jumps over the lazy dog."

  md_to_html(md_text)
  #> [1] "<h1>The story of the fox</h1>\n<p>The quick brown fox <strong>jumps over</strong> the lazy dog.\nThe quick <em>brown fox</em> jumps over the lazy dog.</p>\n"
  ```