Hi all,
I’ve been putting together a little language to learn more about how the Racket
#lang ecosystem works, and I’m hung up on bundling up the language as a
collection. I’m not sure I correctly understand the point where the reader
attaches to the macros that specify how to expand the language forms, and I
want to check.
So, say I have a file semantics.rkt (in mylang/, the main dir of the
collection) defining the macros that make up the language, and a reader
lang/reader.rkt (in the same dir):
#lang s-exp syntax/module-reader
"../semantics.rkt"
#:read my-read
#:read-syntax my-read-syntax
(require "lang/parser.rkt" syntax/strip-context)
;; ...simple defs of my-read and my-read-syntax...
This much works. My question is how to attach the semantics.rkt file to my
reader code correctly if I don’t use syntax/module-reader. If that’s not clear
enough, a more detailed description of the problem follows.
Following the “Installing a Language
<file:///Applications/Racket%20v6.10/doc/guide/language-collection.html>”
section in the Racket Guide, I moved this reader code into a main.rkt file in
the main dir of the collection (call it mylang/):
(module reader racket
(require "lang/parser.rkt" syntax/strip-context)
(provide (rename-out [my-read read]
[my-read-syntax read-syntax]))
(define (my-read in) (syntax->datum (my-read-syntax #f in)))
(define (my-read-syntax src in)
(with-syntax ([(program-part ...) (parse-program-file src in)])
(strip-context
#'(module IGNORE "semantics.rkt"
program-part ...)))))
I can then write
#lang mylang
in another file, and it works as expected iff the file I’m loading is in the
mylang/ directory as well, failing otherwise with an error like this:
/path/to/mylang/main.rkt:17:24: cannot open module file
module path: #<path:/tmp/semantics.rkt>
path: /tmp/semantics.rkt
The module language spec I’ve highlighted in red seems brittle; because
Racket’s looking for semantics.rkt in the directory of the file containing
#lang mylang and not mylang/, I’ve been assuming that’s where the problem is.
Correct me if I’m wrong in this understanding: the #'(module ...) is
effectively replacing the body of whatever program is written in #lang mylang,
so the path-string "semantics.rkt" must be interpreted relative to that
program’s source file.
Anyway, the solution I found is to replace "semantics.rkt" with
mylang/semantics, but that seems like it might be brittle as well; is that the
right way, though? If not, how should I be specifying the connection to the
macros?
Thanks,
Jordan
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