[Johnny_Brahms]

Defmacro is convenient. Debugging when the lack of hygiene leads to weird errors is not.

It happens once ever blue moon, but every time I would kill for a proper syntax-case for CL. Racket's is fine, but I'd be happy with a one like the plain R6RS as well

[progman]

Side effects are no issue if every local variable name in a defmacro is generated with (gensym).

[TeMPOraL]

And if you're tired of doing that by hand, you can... write a macro that'll do that for you. In fact, those were already written, and are available in many libraries as well as featured in many books.

See e.g. Alexandria[0] for with-gensyms (automatically binding your variables to gensyms) and once-only (similar, but ensures the value will be evaluated only once).

Also note that lack of hygiene is actually a useful feature - it allows macros to capture variables from code passed to it as well as the environment they expand it. Some cool stuff can be done that way (some uncool foot-shooting too, though).

--

[0] - https://common-lisp.net/project/alexandria/draft/alexandria....

[sedachv]

> Also note that lack of hygiene is actually a useful feature - it allows macros to capture variables from code passed to it as well as the environment they expand it. Some cool stuff can be done that way (some uncool foot-shooting too, though).

Doug Hoyte's excellent book _Let Over Lambda_ has a lot of examples.

[TeMPOraL]

Oh yes. This book is very fun, in the "what on Earth did he just do here" kind of way.

[Johnny_Brahms]

Syntax-case allows you to introduce bindings into the lexical context (breaking hygiene in a very controlled manner). It does not work with lists, but with syntax objects.

[nyir]

Exactly, you have to specify what you want. Evaluating an expression argument multiple times is probably a mistake, as is not having a new gensym for local variables ... until it is not, e.g. for anaphoric macros (binding some value to "it", https://en.wikipedia.org/wiki/Anaphoric_macro, you can still argue that that's bad style of course).

[ska]

This is an age old (in lisp circles, anyway) argument that has never been resolved, and probably never will. Hygiene has pros and cons, after all.