Macro Expansion Algorithm

Expansion process (from src/lfe_macro.erl:pass_form/3):

1. Check if form is progn → recursively expand all subforms
2. Check if form is eval-when-compile → evaluate at compile time
3. Check if form is include-file/include-lib → read and expand file
4. Check if form is define-macro → add macro to environment
5. Check if form head is macro → expand macro call
6. Otherwise: recursively expand subforms
7. Repeat until no macros remain

Macro lookup (priority order):

1. Local macros (defined in current module)
2. Imported macros (from other modules)
3. Built-in macros (predefined)

Most recently defined wins (LIFO).

Expansion safety:

• Infinite loop detection: Track expansion depth, error if exceeds limit
• Error handling: Collect errors, continue expanding other forms
• Hygiene: Manual (LFE has no gensym - developers are required to protect their macro variables from conflicting with user-space names)