rmarkdown-with-alt-langs-example

---
title: "R Markdown with Alternate Languages"
author: "Curtis Alexander"
output:
  html_document:
    include:
      in_header: header.html
    mathjax: null
params:
  hilang:
    - sas
    - crystal
---

The purpose of this document is to demonstrate that an R Markdown document can display syntax highlighting for languages that are not supported natively by R Markdown.  Highlighting is actually supported by [pandoc](https://pandoc.org/) and the [skylighting](https://hackage.haskell.org/package/skylighting) Haskell library.  A full list of languages supported by pandoc can be found [here](https://github.com/jgm/skylighting/tree/master/xml).

The original reason for working through this was to enable [SAS](https://www.sas.com) syntax highlighting within an R Markdown html document.

For a full description of how this is accomplished and stitched together, refer to my [blog post](https://www.calex.org/blog/r-markdown-syntax-highlighting/).

## Requirements
The following R packages are required for the proposed solution.

* [stringr](https://cran.r-project.org/web/packages/stringr/index.html)
* [htmltools](https://cran.r-project.org/web/packages/htmltools/)

In addition, one will need access to the internet as the solution makes use of `<script>` tags to read in Javascript libraries from a [CDN](https://www.cloudflare.com/cdn/).

## Languages 

### [SAS](https://www.sas.com)
Below is an example of highlighting SAS code.  The code was taken from the [CodeMirror](https://codemirror.net/mode/sas/index.html) example page.

```{r, child="_hilang_setup.Rmd"}
```

```{r, eval=FALSE, hilang="sas"}
libname foo "/tmp/foobar";
%let count=1;

/* Multi line
Comment
*/
data _null_;
    x=ranuni();
    * single comment;
    x2=x**2;
    sx=sqrt(x);
    if x=x2 then put "x must be 1";
    else do;
        put x=;
    end;
run;

/* embedded comment
* comment;
*/

proc glm data=sashelp.class;
    class sex;
    model weight = height sex;
run;

proc sql;
    select count(*)
    from sashelp.class;

    create table foo as
    select * from sashelp.class;

    select *
    from foo;
quit;
```

<br/><br/>

### [Crystal](https://crystal-lang.org/)
Below is an example of highlighting Crystal code.  The code was taken from the [CodeMirror](https://codemirror.net/mode/crystal/index.html) example page.

```{r, eval=FALSE, hilang="crystal"}
# Features of Crystal
# - Ruby-inspired syntax.
# - Statically type-checked but without having to specify the type of variables or method arguments.
# - Be able to call C code by writing bindings to it in Crystal.
# - Have compile-time evaluation and generation of code, to avoid boilerplate code.
# - Compile to efficient native code.

# A very basic HTTP server
require "http/server"

server = HTTP::Server.new(8080) do |request|
  HTTP::Response.ok "text/plain", "Hello world, got #{request.path}!"
end

puts "Listening on http://0.0.0.0:8080"
server.listen

module Foo
  abstract def abstract_method : String

  @[AlwaysInline]
  def with_foofoo
    with Foo.new(self) yield
  end

  struct Foo
    def initialize(@foo : ::Foo)
    end

    def hello_world
      @foo.abstract_method
    end
  end
end

class Bar
  include Foo

  @@foobar = 12345

  def initialize(@bar : Int32)
  end

  macro alias_method(name, method)
    def {{ name }}(*args)
      {{ method }}(*args)
    end
  end

  def a_method
    "Hello, World"
  end

  alias_method abstract_method, a_method

  def show_instance_vars : Nil
    {% for var in @type.instance_vars %}
      puts "@{{ var }} = #{ @{{ var }} }"
    {% end %}
  end
end

class Baz < Bar; end

lib LibC
  fun c_puts = "puts"(str : Char*) : Int
end

baz = Baz.new(100)
baz.show_instance_vars
baz.with_foofoo do
  LibC.c_puts hello_world
end
```

<br/><br/>