first and foremost great documentation & design docs cannot be surpassed as a tool to explain and understand code. and that is entirely language agnostic.
more generally, the most important bits of a particular function to understand is
* what should it be called with
* what should it return
* what side effects might it have
and the "what" here refers to properties in a general sense. types are a good shortcut to signify certain named collections of properties (e.g., the `Int` type has arithmetic properties). but there are other ways to express traits, preconditions, postconditions, etc. besides types
more generally, the most important bits of a particular function to understand is
* what should it be called with
* what should it return
* what side effects might it have
and the "what" here refers to properties in a general sense. types are a good shortcut to signify certain named collections of properties (e.g., the `Int` type has arithmetic properties). but there are other ways to express traits, preconditions, postconditions, etc. besides types