Add support for query languages

DOCS.md

@@ -10,6 +10,7 @@
   + [Edit-in-place](#edit-in-place)
   + [Using packages](#using-packages)
 * [Using .fxrc](#using-fxrc)
+  + [Query language](#query-language)
 * [Formatting](#formatting)
 * [Other examples](#other-examples)
 * [Streaming mode](#streaming-mode)
@@ -130,6 +131,32 @@ curl 'https://api.github.com/repos/facebook/react/commits?per_page=100' \
 > export NODE_PATH=`npm root -g`
 > ```
 
+### Query language
+
+If you want to use query language, for example [jsonata](http://jsonata.org/) you can use helper function like this:
+
+```js
+global.jsonata = expr => require('jsonata')(expr).evaluate
+``` 
+
+And use it like this:
+
+```bash
+curl ... | fx 'jsonata("$sum(Order.Product.(Price * Quantity))")'
+```
+
+Instead you can create next alias in _.bashrc_ file:
+
+```bash
+alias jsonata='FX_APPLY=jsonata fx'
+```
+
+And now all code arguments to `jsonata` will be passed through `jsonata` helper. And now you can use it like this:
+
+```bash
+curl ... | jsonata '$sum(Order.Product.(Price * Quantity))'
+```
+
 ## Formatting
 
 If you need output other than JSON (for example arguments for xargs), do not return anything from the reducer.

reduce.js

@@ -1,6 +1,10 @@
 'use strict'
 
 function reduce(json, code) {
+  if (process.env.FX_APPLY) {
+    return global[process.env.FX_APPLY](code)(json)
+  }
+
   if ('.' === code) {
     return json
   }