arithmetization

I once had the same problem with an old Macbook Air and stubbornly used Ukulele to create a keyboard layout that let me chord around four dead keys with alt and the key directly below. It's not a long term solution, but it might help in a pinch.

I think just tweaking your parse method to use #'string-append and #'~a would be enough to preserve hygiene for your introduced identifiers. datum->syntax will happily work with mixed combinations of syntax-objects and data.

And yes, feel free to do anything with that example and share further. Not enough people have had exposure to Racket's implicit expansion macros. (Is that even what they're called?)

This is cool; I've never seen an example of extending Racket's readtable.

I always imagined implementing string interpolation by overriding the implicit #%datum macro and checking for literal strings. Here's a quick (probably non-idiomatic) example for comparison.

  #lang racket
  
  (require
    (rename-in racket (#%datum core-datum))
    (for-syntax syntax/parse))
  
  (define-syntax (#%datum stx)
    (syntax-parse stx
      [(_ . x:str) (interpolate #'x)]
      [(_ . x)     #'(core-datum . x)]))
  
  (define-for-syntax (interpolate stx)
    (define re            #rx"@{[^}]+}")
    (define (trim match)  (substring match 2 (- (string-length match) 1)))
    (define (to-stx val)  (datum->syntax stx val))
    (define (datum val)   (to-stx (cons #'core-datum val)))
    (define (source text) (to-stx (read (open-input-string text))))
    (let* ([text     (syntax->datum stx)]
           [matches  (regexp-match* re text)]
           [template (datum (regexp-replace re text "~a"))]
           [values   (map (compose source trim) matches)])
      (if (null? matches)
          template
          (to-stx `(,#'format ,template ,@values)))))
  
  42 ;=> 42
  #t ;=> #t
  "1 time" ;=> "1 time"
  
  (define foo 2)
  "@{foo} times" ;=> "2 times"
  "@{(+ foo 1)} times" ;=> "3 times"
  
  (define (scoped foo)
    (define (format . args) "boom!")
    "@{foo} times")
  (scoped 10) ;=> "10 times"