[pfdietz]

It's interesting to see how something like Common Lisp handles the format issue.

In CL, there's a general infrastructure called "compiler macros" that is intended as a hint to the compiler to expand calls as macros at compile time. The macro is also allowed to just leave the form unexpanded, in which case it defaults to an unexpanded function call. And the function can be turned into a value itself and passed around, even if the compiler macro exists.

For CL's format, this means an implementation will typically have a compiler macro (or some similar mechanism) that does an expansion if the format is a string constant.

CL also has a function called formatter that takes a format string and returns a function that acts like (lambda (&rest args) (apply #'format <the format string> args). This function can be implemented as something that expands the format string into code and then compiles the code.

The mechanisms in CL would allow a user to implement the equivalent of a format compiler macro (and formatter) even if the implementation didn't provide them.