Hello,
Suppose I am trying to have my own variant of (define),
which tags text comments to things that it defines.
I am keeping the comments in a hashtable for whatever
purpose, and in the following example I am just printing
them to the standard output:
~~~~~ defcom.rkt
#lang racket
(define-for-syntax comments (make-hash))
(define-syntax (def-with-comment stx)
(syntax-case stx ()
((_ (name comment . params) . body)
(hash-set! comments (syntax->datum #'name) (syntax->datum #'comment))
#'(define (name . params) . body))))
(def-with-comment (my+ "addition" a b) (+ a b))
(def-with-comment (my- "subtraction" a b) (- a b))
(begin-for-syntax
(for (((name val) comments))
(printf "~a: ~a\n" name val)))
(printf "~a\n" (my- (my+ 3 4) 2))
That works great and prints:
my+: addition
my-: subtraction
5
The trouble starts when I split the macro, the definitions,
and the main program into separate modules.
~~~~~~~~ defcom1.rkt
#lang racket
(provide def-with-comment
(for-syntax comments))
(define-for-syntax comments (make-hash))
(define-syntax (def-with-comment stx)
(syntax-case stx ()
((_ (name comment . params) . body)
(hash-set! comments (syntax->datum #'name) (syntax->datum #'comment))
#'(define (name . params) . body))))
~~~~~~~~ defcom2.rkt
#lang racket
(require "defcom1.rkt")
(provide my+ my-)
(def-with-comment (my+ "addition" a b) (+ a b))
(def-with-comment (my- "subtraction" a b) (- a b))
~~~~~~~~ defcom3.rkt
#lang racket
(require "defcom1.rkt")
(require "defcom2.rkt")
(begin-for-syntax
(for (((name val) comments))
(printf "~a: ~a\n" name val)))
(printf "~a\n"(my- (my+ 3 4) 2))
It does not print my hash table.
I understand why it happens: when defcom2 compiles, it gets its own
instance of defcom1, which is "forgotten" during the compilation of
defcom3, and defcom3 gets a fresh instance of defcom1 with
an empty hashtable.
However, I do not see how to fix that. Does anybody?
What is the recommended way to do that sort of thing in Racket?
Regards,
Dmitry
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