String Closures

I‘m not sure I’ve ever encountered the notion that a string formatting function produces a closure over the function produced by the format string, and the arguments as the lexical environment. Let‘s get a concrete example here:

(printf "%d. %s owes $.02f\n" index name debt)

is effectively:

((lambda (index name debt)
   (print
      (string-append
          (%d index)
          ". "
          (%s name)
          " owes $"
          (%f ".02" debt))))
 index name debt)

That is assuming that %d %s and %f were functions that behaved appropriately. This isn’t far off since Racket has functions like this, named differently. Rust‘s format strings are implemented as a macro, format!, but it doesn’t appear to me to produce a closure, rather some other type. As I‘m not a crustacean, I can’t be sure that the result isn‘t exactly what I’m suggesting – it‘s certainly in spirit similar.

Anyway, the point of this is that we might take it farther and construct curried format functions that return formatted strings. A “string closure” if you will.