alt Hacker NewsHomoiconicity is orthogonal to local reasoning. It just means the syntax is represented by the native data format, nested lists. This does make code generation very straightforward with list processing primitives.
Mutation in scheme is possible, via set!, and set-car! and set-cdr!, but it's not recommended. Functional program design side-steps the issue.
see also:
SICP: 3.1.3 The Costs of Introducing Assignment
https://sarabander.github.io/sicp/html/3_002e1.xhtml#g_t3_00...
Yes, I know they're orthogonal. But every example of using macros I see in lisp is either some horrendous non-local logic, or something that can be done better using simpler tools. Where's the killer use case that clearly is good software engineering and not papering over the lack of another feature?