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
#: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 
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)])
       #'(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 


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