When is macro expansion performed?
macros, racket
Solution
Although a Racket expert might correct me, my understanding is that the main stages are:
A read pass that processes the input characters into a syntax object.
An expansion pass that recursively expands the syntax object, including using user-defined macros.
Evaluation. (JIT compilation happens during evaluation, whenever a not-yet-compiled function is called.)
In other words the REPL (read eval print loop) is really more like a REEPL (read expand eval print loop).
For an extreme level of detail see Language Model including e.g. the Syntax Model section.
You mentioned "type-checking".
- Plain Racket (e.g. `#lang racket`) is dynamically typed and checking is done at runtime.
- Typed Racket (e.g. `#lang typed/racket`) does static type-checking during expansion: the Typed Racket system is implemented via macros. See Section 10, "Implementation", of Sam Tobin-Hochstadt's dissertation.
(Edited to note the JIT is actually part of evaluation, not a separate stage.)
Problem
I'm learning about macros in Racket (language successor of Scheme). There is no mentioning of when the macro expansion is performed. On page 17 of this document I found a paragraph that says it happens before type-checking, evaluation and compiling. So if I understand correctly, macro expansion occurs right after building the abstract syntax tree (AST)?