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gensym prevents the macro from accidentally messing with the macro user, but does not prevent the macro user from messing with the macro. For example, a macro user can redefine if or something like that. (The question "why would anybody do that" is irrelevant. This is a simple example that demonstrates that it's possible, and it's tricky to reason about non-hygienic macros)

Phil
– Phil

2016-11-04 03:08:41 +00:00
Commented Nov 4, 2016 at 3:08
2

Unhygienic macros are certainly useful. I'm not sure about Scheme, but Racket has lots of "hygiene-bending" operations. The language's macros are hygienic by default. They just make you very conscious when you break hygiene.

Phil
– Phil

2016-11-04 03:10:21 +00:00
Commented Nov 4, 2016 at 3:10

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