What's the purpose of define-transformation?

[cireu]

In the compiler, define-transformation is only used for defining backquote. It seems to be a way to define some kind of Lisp-to-Lisp transformation.

However, we can define backquote as macro in the early place of boot.lisp, and it actually doesn't harm the bootstrappability.

I'd propose to remove define-transformation in compiler, remove it can help reduce code and improve consistency, but I want to understand its design purpose first, and confirm whether we have other place to utilize define-transform.

[kchanqvq]

@cireu discussed with me before and this looks sensible to me. @davazp what do you think?

[davazp]

Sorry I thought I replied to this.

Sure, we can remove it. It probably is just some machinary from early versions of jscl before macro support was mature enough.

If you check the simple-bootstrap tag from 2013 (!), it contains a 1300 single file bootstrappable version of jscl, and define-transformation was already there and used for backquote like this:

(defmacro backquote (form)
  (backquote-expand-1 form))

(define-transformation backquote (form)
  (backquote-expand-1 form))

So we probably used define-transformation for bootstrap, and defmacro for runtime. We improved the bootstrapping code since then it seems!