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The emacs eshell is an interactive shell for entering commands written in elisp. I like it because it feels like a normal emacs buffer and I can easily move around and copy and paste, without switching to a copy mode. It loses many of the features of bash, but when I need them I can use bash, inside or outside of emacs.

I had a hard time figuring out how to set the path it uses when I type commands, though. I wound up finding a way that worked for me by reading the source of the which function and then the code of eshell-search-path, which the which function uses to find executables in the path.

The variable is eshell-path-env and it’s a colon-separated list of directories. I needed to add my nodebrew directory to it, and I did so by adding the following to ~/.emacs.d/init.el:

(setq eshell-path-env (concat "/Users/bat/.nodebrew/current/bin" ":" eshell-path-env))

I’m not sure that this is the best answer, but it took me a while to find and answer that worked so I thought I’d share it.

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XML/HTML are centered around elements. An element is something that has an opening tag and a closing tag, or simply has a single self-closing tag (The slash before the closing angle bracket is required in XML and XHTML but not HTML). For example, this has six elements:

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8" />
    <title>Hello, world.</title>
  </head>
  <body>
    <p>Hello, world.</p>
  </body>
</html>

In this example each tag name is only used once. The elements are (by order of first appearance) html, head, meta, title, body, p. The DOCTYPE definition is special and is not considered to be an HTML or XML element. The charset part of this document is an attribute.

What does element mean in JSON? Something a bit different. An XML element is a compound data type. A JSON element is part of a compound data type.

If you look at the white box on the right part of json.org detailing the grammar, you can see that it has names for items in JSON’s compound data types, objects and arrays. An item in an object is called a pair, and an item in an array is called an element.

It helps when building APIs for processing data formats to have names for things. The terminology for XML is used in XML tools, and has made them easier to understand. For instance, the jQuery API docs use the terms element and attribute heavily.

I think the JSON community should adopt the terms pair and element and use them more frequently, to enhance understanding of the data. It’s useful to talk about a pair rather than a key and a value, because when you add something to a JavaScript object that’s what your adding. You aren’t adding just a value. A JavaScript array can include multiple copies of the same value, so when you’re removing a single occurrence of a value, it makes more sense to say you’re removing an element than removing a value.

JSON has been popular for years now, in many vital technology communities, but it is still lacking in processing support compared to XML. I think clear terminology is one thing that XML has right, and indeed the JSON spec has clear terminology. What’s lacking is widespread use of the terminology.

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Here’s a copy of the email I sent to the CouchDB users mailing list:

I made a couple of npm (node.js) modules for editing CouchDB design documents that involves fewer files than python CouchApp, but like python CouchApp supports two-way sync. The function source is left intact when converting between JavaScript source and JSON. The JavaScript source version just shows it in an embedded function expression, which makes it syntax highlightable.

http://benatkin.com/2012/09/04/js2json-and-json2js/
https://github.com/benatkin/js2json
https://github.com/benatkin/json2js

Here’s a quick example. If I stick this in books.js:

module.exports = {
  "views": {
    "author": {
      "map": function(doc) {
        if (doc.type == 'book')
          emit(doc.author, null);
      }
    },
    "title": {
      "map": function(doc) {
        if (doc.type == 'book')
          emit(doc.title, null);
      }
    }
  }
}

…and run this (after npm install json2js js2json):

var js2json = require('js2json');
var json2js = require('json2js');
var fs = require('fs');

var jsSource = fs.readFileSync('books.js', 'utf8');
var jsonValue = js2json.convert(jsSource);
fs.writeFileSync('books.json', JSON.stringify(jsonValue, null, 2) + "\n");
var jsSourceFromJson = json2js.convert(jsonValue);
fs.writeFileSync('books-from-json.js', jsSourceFromJson + "\n");

…I get the following in books.json:

{
  "views": {
    "author": {
      "map": "function(doc) {\n  if (doc.type == 'book')\n
emit(doc.author, null);\n}"
    },
    "title": {
      "map": "function(doc) {\n  if (doc.type == 'book')\n
emit(doc.title, null);\n}"
    }
  }
}

…and books-from-json.js is exactly the same as books.js.

I explain it more in my blog post (linked at the top of this message). I need to add a cli tool that syncs, a way to handle attachments, and a way to handle embedded multiline strings for it to be a full-featured design doc editor. I have much bigger plans for this, though: I want to break up CouchApps into a bunch of smaller documents! The source and tests for these two modules is programmed in the same style. I think storing functions in JSON makes CouchDB just a little bit like Smalltalk, with a much more familiar language.

Thanks for reading. Feedback welcome and appreciated.

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I made a couple of small node.js modules to help me develop couchapps.

CouchApp is two things: a concept and a tool. The concept is an application that runs on CouchDB, using its API. The API has three basic components for presenting data (it has others for editing data but that isn’t covered in this post):

  • views: A view in CouchDB is a Map and optionally a Reduce function, which enables indexing JSON documents using the powerful MapReduce programming model.
  • lists: A list is a function that renders documents from a view, into an any format (commonly HTML).
  • shows: A show function renders a single document, into any format.

With these simple functions, a blog or a photo gallery can be made viewable. The URLs can get a bit awkward, but CouchDB provides a rewrites feature to solve it.

These functions go into a CouchDB design document. CouchDB is a JSON database, and a design document is a JSON document that contains functions as strings. A single design document, with attachments for CSS, which can be served directly to the web browser, can provide access to data without relying on client-side JavaScript (instead using server-side JavaScript).

The tool is a python command-line utility that maps a CouchDB design document to a directory structure. It can clone a design document directly from the database. It breaks it into a lot of little files, including a separate JavaScript file for each function.

This can be a lot of files, when there is one file for each function. Here is the CouchOne pages wiki CouchApp. It has a lot of views.

Mikeal Rogers had perhaps the first solution to this problem: node.couchapp.js. It runs on node.js and allows programmatic building of a design document, and puts functions in strings to prepare the JSON using Function.toString(). This loses the python CouchApp’s advantage of being able to go back and forth from file to CouchDB without losing anything.

I wanted something that could sync back and forth and is more like the original JSON than python’s CouchApp. To make it usable, I need functions shown across multiple lines with syntax highlighting. My hack was to convert the JavaScript to JSON. With CommonJS I can convert JSON to JavaScript easily, just by adding module.exports = to the front of the file. I can then replace the function strings with the direct value of the strings. To go from JavaScript to JSON I need to get the original function source. With JavaScript’s fn.toString(), where fn is a function, I get the source without the comments. I want the comments. It also isn’t indented properly. With Esprima I wrote code to extract the raw function source and fix up the indentation. Examples of this are in the READMEs of the two projects, json2js and js2json.

The projects below are still in early development and barely tested, but I’m putting them to use right now, by finally putting one of my fancy domain names to good use. ;) In the meantime, if this interests you, please check them out and give me feedback.

Repositoryjson2js
Ownerbenatkin
Repositoryjs2json
Ownerbenatkin