Pre-processing

As with all type-checkers, multiple passes must be performed to ensure that all types are defined, and all functions/variables are given their types, before type-checking actually begins. et performs 3 distinct phases:
1. Identification - Identify all of the expressions that need to be pre-processed
2. Pre-processing - Pre-process all of the identified expressions
3. Checking - Perform type-checking

Identification is performed by looping through all sexps in the current buffer (and all required buffers), checking the car of the expression for an identifier function, and calling that identifier function. An identifier function returns a plist which describes how to pre-process the expression.
To add an identifier to a symbol, use et-set-identifier:

(et-set-identifier #'defun #'et:identify-defun)