arc> (mkdir "foo")
  Error: "Function call on inappropriate object nil (\"foo\")"

As for merging, there are already some commits in stable that aren't in master, because their functionality was based on Anarki-only features in master. Merging would try to merge those as well, which may have unintended consequences. It might also double up a bunch of the commits in master, which would be unfortunate.

That would be a one-time headache with the first merge. After that, as long as bugfixes go into the stable branch, you won't have that problem. (Just had a quick look, it seems like it's currently a fairly trivial merge with only a few minor conflicts - I think git is doing the right thing for you here, but I don't know arc well enough to be sure).

> I would love to have nice history. I'm all ears for suggestions.

Basically, imho, splitting a tree is work and merging shouldn't be.

So by putting the commits in the right place to start with, you're avoiding work (and errors, and people checking with other people to see if that is supposed to be like that, etc).

You're essentially preserving more information as to the purpose of the fix (this is a bugfix) in a way that the tools can get hold of.

  (defsyntax insert-file-here ()) ; dunno, never figured out scheme macros

  (module arc-exe mzscheme
    (insert-file-here "ac.scm")
  )

  (progn
    (provide (all-defined))
    ...
    (define (ac s env)
    ...)
  )

The alternative is to have the macros generate the (module ...) code, and insert the code inside the modules of ac.scm and as.scm and what else arc needs.

I hacked together a short version of arc-exe.scm that worked just fine importing from ac.scm. The only problem with that version was that it wasn't a module, and thus couldn't be compiled by mzc. I couldn't make it a module because scheme complained when brackets.scm tried to override read and read-syntax. (Apparently overriding imported bindings only works outside modules.) And when I tried to modify or not include brackets.scm, it would complain that it couldn't find the module ac.

  (define (ac-call fn args env)
   (let ((macfn (ac-macro? fn)))
    (cond (macfn
           (ac-mac-call macfn args env))
          ((and (pair? fn) (eqv? (car fn) 'fn))
           `(,(ac fn env) ,@(map (lambda (x) (ac x env)) args)))
          ((= (length args) 0)
           `(ar-funcall0 ,(ac fn env) ,@(map (lambda (x) (ac x env)) args)))
          ((= (length args) 1)
           `(ar-funcall1 ,(ac fn env) ,@(map (lambda (x) (ac x env)) args)))
          ((= (length args) 2)
           `(ar-funcall2 ,(ac fn env) ,@(map (lambda (x) (ac x env)) args)))
          ((= (length args) 3)
           `(ar-funcall3 ,(ac fn env) ,@(map (lambda (x) (ac x env)) args)))
          ((= (length args) 4)
           `(ar-funcall4 ,(ac fn env) ,@(map (lambda (x) (ac x env)) args)))
          (#t
           `(ar-apply ,(ac fn env)
                      (list ,@(map (lambda (x) (ac x env)) args)))))))

  (define (ac-call fn args env)
  (let ((macfn (ac-macro? fn)))
    (if macfn
      (ac-mac-call macfn args env)
      (let ((afn (ac fn env))
            (aargs (map (lambda (x) (ac x env)) args))
            (nargs (length args)))
        (cond
          ((eqv? (xcar fn) 'fn)
           `(,afn ,@aargs))
          ((and (>= nargs 0) (<= nargs 4))
           `(,(string->symbol (string-append "ar-funcall" (number->string nargs)))
              ,afn ,@aargs))
          (#t
           `(ar-apply ,afn (list ,@aargs))))))))

  (define (ac-fn args body env)
   (if (ac-complex-args? args)
      (ac-complex-fn args body env)
      `(lambda ,(let ((a (ac-denil args))) (if (eqv? a 'nil) '() a))
         'nil
         ,@(ac-body body (append (ac-arglist args) env)))))

  (define (ac-fn args body env)
   (if (ac-complex-args? args)
      (ac-complex-fn args body env)
      `(lambda ,(let ((a (ac-denil args))) (if (eqv? a 'nil) '() a))
         ,@(ac-body* body (append (ac-arglist args) env)))))

  (define (ac-fn args body env)
   (if (ac-complex-args? args)
      (ac-complex-fn args body env)
      `(lambda ,(let ((a (ac-denil args))) (if (eqv? a 'nil) '() a))
         'nil
         ,@(ac-body body (append (ac-arglist args) env)))))

  (define (ac-fn args body env)
   (if (ac-complex-args? args)
      (ac-complex-fn args body env)
      `(lambda ,(let ((a (ac-denil args))) (if (eqv? a 'nil) '() a))
         ,@(ac-body* body (append (ac-arglist args) env)))))

Although I suppose you could actually use --warning-blatant-self-proclamation-- my p-m: macro:

  (p-m:def matrix
    (,(s (is s settersym)))
      writerfunction
    (i j)
      (readerfunction i j)
    x (err "argument error"))