Hi all,
I'm programming in Racket for many years and still haven't used macros
or delved into how they work. Kind of embarrassing... anyway, it should
be clear what I want to achieve in the code below. I like to wrap a
module around framework/preferences, abstracting from the preference
implementation while at the same time exporting symbols of the form
pref:identifier - I want unknown preferences to be detected at compile
time.
The pref helper macro works. But I'm doing something obviously wrong in
defpref, since it gives an error "db-path: unbound identifier in
module". How do I *define* the derived identifier, as in name ->
pref:name, with a syntax macro? Does "definition-key" have to be a
macro as well?
Best,
Erich
-------
#lang racket
(require framework/preferences)
(provide init-preferences const:app-name const:app-version
pref:db-path)
(define const:app-name "Virtual Assistant")
(define const:app-version 1.0)
(define default-datapath (build-path (find-system-path 'home-dir)
"Documents" "va"))
(define *defaults* '())
(define (lookup-key ident)
(string->symbol (string-append "va:" (symbol->string ident))))
(define (definition-key ident)
(string->symbol (string-append "pref:" (symbol->string ident))))
(define-syntax pref
(syntax-rules ()
[(pref ident) (let ((key (lookup-key ident)))
(unless (preferences:default-set? key)
(init-preferences)) (preferences:get key))]
[(pref ident value) (let ((key (lookup-key ident)))
(unless (preferences:default-set? key)
(init-preferences)) (preferences:set key value))]
[(pref ident expr test?)
(set! *defaults* (cons (list (lookup-key ident) expr test?)
*defaults*))]))
(define-syntax defpref
(syntax-rules ()
[(defpref ident default test?) (begin
(define (definition-key ident)
(case-lambda
[() (pref ident)]
[(value) (pref ident value)]))
(pref ident default test?))]))
(defpref db-path default-datapath path?)
(define (init-preferences)
(make-directory* default-datapath)
(for-each
(lambda (triple)
(preferences:set-default (first triple) (second triple) (third
triple))) *defaults*))
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