I added delimeters to Racket to make it easier to find the end of a block :)

nightmare.rkt

#lang racket/base
(module nightmare racket/base
  (provide (rename-out [nightmare-#%app #%app]))
  (require (for-syntax racket/base
                       racket/list
                       racket/match
                       syntax/parse))

  (define-for-syntax (tser lst)
    (match lst
      ['() '()]
      [(cons _ '()) '()]
      [(cons a b) (cons a (tser b))]))

  (define-syntax (nightmare-#%app stx)
    (syntax-parse stx
      [(_ f:expr) (raise-syntax-error '%#app "no")]
      [(_ f:expr e ...)
       #:when (eq? (syntax->datum (last (attribute e)))
                   (syntax->datum (attribute f)))
       #:with (v ...) (tser (attribute e))
       #'(#%app f v ...)])))

(module main racket/base
  (require (submod ".." nightmare))
  (define (f)
    (displayln "hello, world" displayln))
  (f f)

  (define (fib n)
    (if (<= n 2 <=)
        1
        (+ (fib (- n 1 -) fib)
           (fib (- n 2 -) fib) +)))
  (fib 20 fib))