Print the name of a variable

Question

Is it possible in Scheme R6RS to print the name of a variable? I mean:

(define (f) 
   (lambda (arg)
      (display ( *name* arg))))

Such that:

(define my-var 3)
(f my-var) ; => displays the string "my-var")

Answer 1

You need a syntactic extension (a.k.a. macro) to prevent evaluation:

#lang r6rs
(import (rnrs))

(define-syntax f
  (syntax-rules ()
    [(_ x) (display 'x)]))

(define my-var 3)
(f my-var)

outputs

my-var

Racket's macro-expander shows the effects of the transformation:

(module anonymous-module r6rs
  (#%module-begin
   (import (rnrs))
   (define-syntax f (syntax-rules () [(_ x) (display 'x)]))
   (define my-var 3)
   (f my-var)))

->  [Macro transformation]

(module anonymous-module r6rs
  (#%module-begin
   (import (rnrs))
   (define-syntax f (syntax-rules () [(_ x) (display 'x)]))
   (define my-var 3)
   (display 'my-var)))

which, of course, means that you could simply write

(display 'my-var)

to get the same result ;-)