custom compiler docs

README.md

@@ -144,6 +144,36 @@ parser:run(second_fn, nil, buffer, #buffer)
 print(table.concat(buffer)) -- print 'Hello World'
 ```
 
+## Custom compiler
+
+If you need to customize the Lua code that is generated by etlua to integrate
+with your own output buffers then you can provide a custom compiler.
+
+You can extend `etlua.Compiler` and override it's methods to control the
+output. See <https://github.com/leafo/etlua/blob/master/etlua.moon#L42> for the
+implementation of the default compiler
+
+For an example we'll create a debug compiler that prints whenever a template is
+executed.
+
+```moonscript
+-- create a custom compiler
+import Compiler from require "etlua"
+
+class DebugCompiler extends Compiler
+  header: =>
+    @push 'print("Running template")\n'
+    super
+
+-- try it out
+import Parser from require "etlua"
+
+print Parser!\compile_to_lua "hello", DebugCompiler
+```
+
+`compile_to_lua` takes an optional second argument of the compiler class to
+use.
+
 ## License
 
 MIT, Copyright (C) 2014 by Leaf Corcoran