SRFI-105 (curly-infix) mentions another notation, "sweet-expressions".  Sweet-expressions build on top of SRFI-105 (curly-infix), adding (1) indentation processing, and (2) neoteric-expression support *outside* of curly braces.  Here's an example of sweet-expressions:
define factorial(n)
! if {n <= 1}
!   1
!   {n * factorial{n - 1}}

You can see the current early draft of the sweet-expression SRFI here:
  https://sourceforge.net/p/readable/code/ci/6df69c79786729a11bf3859fc3f24e4a5bd1b1dc/tree/SRFI-sweet.html?format=raw

If you're interested in helping to get it ready for a SRFI submission, please join us in the readable-discuss mailing list:
  https://lists.sourceforge.net/lists/listinfo/readable-discuss

 --- David A. Wheeler