Static analysis in Elixir - how to have more static information?

You can do it via the accumulator argument. Honestly though I just encode my own processing as just normal function calls, Elixir’s AST is really simple.

I could push values to the accumulator in the prewalk function, but how can I pop them at the right time? Because for example in the prewalk it will read a node and then its children, and then it will go to its sibling node. How can I tell I’m at the last child so that I can pop information from the stack? For example suppose the stack is tracking nested function calls

Same way as you would anywhere else, just pop the values and return the new structure with the popped values removed.

Use traverse so you get both ‘up’ and ‘down’ calls.

Are pre and post arguments in traverse the push/pop down/up calls?

Yep, pre means it is run ‘before’ recursing down, post means it is run ‘after’ recursing down, so you will push environment in on pre and pop the environment off in post.

Also, the prewalk and postwalk are just like using traverse but doing nothing in the other one, so prewalk is like using the pre in traverse while doing nothing in post (fn x -> x end) and likewise for the other way.

Cool thanks! But you roll your own traversals usually?

I tend to do slightly more complex work than most though… ^.^;