md-babel.el: Execute block-at-point in markdown-mode

Brings the joy of org-mode babel code block execution to Markdown documents in Emacs using md-babel

Usage

Create a key binding for md-babel-execute-block-at-point. In markdown-mode, C-c C-c is already bound to markdown-mode-command-map, from which you can export and check the document. I suggest you add another C-c to it, so that you can press this key combination 3 times (instead of org's 2):

(define-key markdown-mode-command-map (kbd "C-c") #'md-babel-execute-block-at-point)

Now you can put your point into any GitHub-flavored Markdown code block and evaluate it.

Example

For example, evaluating the Emacs Lisp block above, which (repeated literally) is:

```elisp
(define-key markdown-mode-command-map (kbd "C-c") #'md-babel-execute-block-at-point)
```

... will produce a JSON response from the md-babel program like this:

{
  "range": {
    "from": { "line": 12, "column": 1 },
    "to": { "line": 12, "column": 1 }
  },
  "error": "Configuration missing to execute code with language “elisp”.",
  "replacementRange": {
    "from": { "line": 11, "column": 1 },
    "to": { "line": 19, "column": 4 }
  },
  "replacementString": "```elisp\n(define-key markdown-mode-command-map (kbd \"C-c\") #'md-babel-execute-block-at-point)\n```\n\n<!--Error:-->\n```\nConfiguration missing to execute code with language “elisp”.\n```"
}

The "replacementString" repeats the original code block and appends an error block, meant to replace the buffer substring denoted by "replacementRange", so that it is inserted into the same buffer. The error block will look like this:

<!--Error:-->
```
Configuration missing to execute code with language “elisp”.
```

Well, that's a bummer, so ...

Adding Elisp Support to md-babel

... here's how you can teach md-babel to run your Emacs Lisp code.

Create a configuration JSON file with this content in ~/.config/md-babel/config.json

{
  "elisp": {
    "path": "/usr/bin/env",
    "defaultArguments": ["emacsclient", "--eval"]
  }
}

This assumes you're running Emacs server.

Note

Emacs server allows you to evaluate Emacs Lisp code in the context of your currently running instance. That is required so that evaluating the code block with the define-key function call actually affects the Emacs instance you're currently running like M-x eval-expression.

Then try to run the code block with M-x md-babel-execute-block-at-point.

If you want to execute a code block in a self-contained Emacs that doesn't depend on your config, use batch execution mode instead:

{
  "elisp": {
    "path": "/usr/bin/env",
    "defaultArguments": ["emacs", "--batch", "--eval"]
  }
}

With that setting, you can execute this code block and get the message from standard output routed into your result block:

(message "Hello, Emacs!")