That's true but it's not the most important aspect of macros. Macros let you define a new language that describes your problem solution more directly than you can in raw Lisp. In other words they let you create a Domain-Specific Lamguage (DSL). You can create DSLs in other languages too but it's so difficult that it's uncommon. In Lisp it's so easy that DSLs are a primary programming technique.

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klibertp 4 hours ago | parent | next [-]

I don't think that moving the evaluation to compile time is something you can just ignore when discussing macros. It's an important differentiator between macros and Fexprs[1].

IME, the primary use case for macros in Lisps is language extension, a step before a DSL. For every `loop` there are thousands of `with-x` macro implementations. See the macro-writing macros in Alexandria/Serapeum for the most common patterns.

Also, some dynamic languages (Io, Prolog, Groovy) support DSLs through non-macro mechanisms. DSLs in those languages are as easy (or easier) to implement as in Lisps; however, they tend to be less performant. So, again, compile-time macro execution does matter for the DSL use case, too.

[1] https://en.wikipedia.org/wiki/Fexpr

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ux266478 3 hours ago | parent | next [-]

In the case of Prolog, term and goal expansion are arbitrary compile-time execution mechanisms, completely isomorphic with macros, and are referred to as macro mechanisms.

The characterization of it not being "compile-time macro execution" is strange, what do you think these predicates are doing?

	▲	klibertp 3 hours ago \| parent [-]
		Good point. I was thinking about meta-interpreters (and it's still possible I misunderstood or misremembered how they work!), but you're right; I should have at least been more precise.

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carlosneves 2 hours ago | parent | prev [-]

Thanks for linking to Fexpr's. I've thinking about "functions with lazily evaluated arguments" recently, and trying to understand how they are different from macros. So I was basically thinking about fexprs.

I have some reading to do, but overall it seems like macros are favored instead of fexprs. Macros completely avoid some environment handling issues.

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throw-qqqqq 2 hours ago | parent | prev [-]

I don’t disagree, but I think this is a matter of taste: i.e. which aspect you’d consider more important.

You can create DSLs without macros, for example by parsing and interpreting at runtime, but macros let you move much of that logic to compile time.

For me, that's the killer feature: writing code that looks dynamic or interpreted, but ends up as compiled code.