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Note that this cannot be written as a function only because Clojure uses strict (call-by-value) evaluation everywhere and has no way to change this (other than

Note that this cannot be written as a function only because Clojure uses strict (call-by-value) evaluation everywhere and has no way to change this (other than Macros). In theory languages could provide annotations to allow a user to specify whether parameters are call-by-value or call-by-need. Haskell and Scala both provide this. But I don't think this is a bad example at all, I tend to think of macros as "extending the language/compiler", since they have access to the abstract syntax tree of their inputs, which is what is being done here.

roenxi 5y ago
Yeah. And for the interested reader, this is unique power of macros. It doesn't matter what specific combination of language features are supported. Macros mean you can implement things anyway. It doesn't really matter what the evaluation logic of the language is, a macro can create syntax that does what you want it to. If there is a macro system available, a new operator can be implemented in any language. If there is no macro system, it depends what features the language supports.