Am Do., 13. Aug. 2020 um 02:40 Uhr schrieb Alex Shinn <xxxxxx@gmail.com>:
>
> OK, you can leverage the internal Chibi binding renaming mechanism here,
> but each implementation will need it's own low-level tricks.  Note you had to
> resort to C code to implement this.
>
> The (auto) module can be implemented in a few lines of Scheme in meta-7.scm.

I hope you agree with me that you don't want to derive any general
conclusions from this as this is very Chibi specific. My
implementation is also no more than a few lines in Scheme code and the
only C code I needed was absolutely trivial and to make a C function
available through the FFI.

If I did the same implementation in Chez, say, it would also only be a
few lines in its syntax.ss. The same is true for any psyntax-based
implementation like Guile.

I don't want to say that it is less complicated to implement a new
binding form, but it isn't more complicated either.

There are at least two scenarios where we want to have a local binding
constructs:

(1) If some macro has to auto-generate an auxiliary keyword on the fly
(depending on the user input), it cannot locally import an (auto)
module (because we have no local imports for some good reasons), but a
binding form like "define-keyword" would suffice.

(2) If user code imports two modules A and B from two different
sources. Say, A, defines some procedure "->", but B uses "->" as an
auxiliary syntax keyword. I can only import both by renaming either
"->" of A or B, which would lead locally to code using A or B that is
harder to read because of the renamed identifier. With
"define-keyword", I can just import B's "->" under any name and
locally bring it back into scope under the original name "->".

> Another advantage of the (auto) module is it can be implemented as a
> normal R7RS library for any fixed set of keywords.  You can have a build
> target to auto-generate it, making it usable with any implementation which
> doesn't support it natively.

This does not work for more than one source that wants to use this trick.

In any case, maybe a future SRFI on this can provide both in a compatible way:

- A classical Scheme binding form like "define-keyword".
- A "magic" module like "(auto)".

Marc

> On Thu, Aug 13, 2020 at 4:46 AM Marc Nieper-Wißkirchen <xxxxxx@nieper-wisskirchen.de> wrote:
>>
>> At the end of this email is a patch for a quick-and-dirty
>> implementation of "define-keyword" for Chibi.
>>
>> Please see the file lib/chibi/keyword-test.sld to see how it is used.
>>
>> (define-keyword <id> <name>)
>>
>> binds <id> to auxiliary syntax identified by the symbol <name>.
>>
>> -- Marc
>>
>> commit a61d1fe5f36e7f53f990df8eceb3dc7ad89d16cb
>> Author: Marc Nieper-Wißkirchen <xxxxxx@nieper-wisskirchen.de>
>> Date:   Wed Aug 12 21:40:40 2020 +0200
>>
>>     Implement define-keyword
>>
>> diff --git a/lib/chibi/ast.c b/lib/chibi/ast.c
>> index 13d776ed..28812f37 100644
>> --- a/lib/chibi/ast.c
>> +++ b/lib/chibi/ast.c
>> @@ -297,6 +297,14 @@ sexp sexp_env_push_op (sexp ctx, sexp self,
>> sexp_sint_t n, sexp env, sexp name,
>>    return SEXP_VOID;
>>  }
>>
>> +#if SEXP_USE_RENAME_BINDINGS
>> +sexp sexp_env_rename_op (sexp ctx, sexp self, sexp_sint_t n, sexp
>> env, sexp key, sexp value) {
>> +  sexp_assert_type(ctx, sexp_envp, SEXP_ENV, env);
>> +  sexp_assert_type(ctx, sexp_idp, SEXP_SYMBOL, key);
>> +  return sexp_env_rename (ctx, env, key, value);
>> +}
>> +#endif
>> +
>>  sexp sexp_core_code_op (sexp ctx, sexp self, sexp_sint_t n, sexp c) {
>>    sexp_assert_type(ctx, sexp_corep, SEXP_CORE, c);
>>    return sexp_make_fixnum(sexp_core_code(c));
>> @@ -726,6 +734,9 @@ sexp sexp_init_library (sexp ctx, sexp self,
>> sexp_sint_t n, sexp env, const char
>>    sexp_define_foreign(ctx, env, "env-syntactic?-set!", 2,
>> sexp_env_syntactic_set_op);
>>    sexp_define_foreign(ctx, env, "env-define!", 3, sexp_env_define_op);
>>    sexp_define_foreign(ctx, env, "env-push!", 3, sexp_env_push_op);
>> +#if SEXP_USE_RENAME_BINDINGS
>> +  sexp_define_foreign(ctx, env, "env-push-rename!", 3, sexp_env_rename_op);
>> +#endif
>>    sexp_define_foreign(ctx, env, "core-code", 1, sexp_core_code_op);
>>    sexp_define_foreign(ctx, env, "object-size", 1, sexp_object_size);
>>    sexp_define_foreign(ctx, env, "immutable?", 1, sexp_immutablep_op);
>> diff --git a/lib/chibi/ast.sld b/lib/chibi/ast.sld
>> index 2856f656..dac80aeb 100644
>> --- a/lib/chibi/ast.sld
>> +++ b/lib/chibi/ast.sld
>> @@ -32,7 +32,7 @@
>>     bytecode-name bytecode-literals bytecode-source
>>     port-line port-line-set! port-source? port-source?-set!
>>     extend-env env-parent env-parent-set! env-lambda env-lambda-set!
>> -   env-define! env-push! env-syntactic? env-syntactic?-set! core-code
>> +   env-define! env-push! env-push-rename! env-syntactic?
>> env-syntactic?-set! core-code
>>     type-name type-cpl type-parent type-slots type-num-slots
>>     type-printer type-printer-set!
>>     object-size object->integer integer->immediate gc gc-usecs gc-count
>> diff --git a/lib/chibi/keyword-test.sld b/lib/chibi/keyword-test.sld
>> new file mode 100644
>> index 00000000..d39824ee
>> --- /dev/null
>> +++ b/lib/chibi/keyword-test.sld
>> @@ -0,0 +1,27 @@
>> +(define-library (chibi keyword-test)
>> +  (export run-tests)
>> +  (import (scheme base) (chibi keyword) (chibi test))
>> +  (begin
>> +    (define (run-tests)
>> +      (test-begin "keyword")
>> +
>> +      (test-group "define-syntax literals"
>> +    (define-keyword foo foo)
>> +    (define-keyword bar foo)
>> +    (define-keyword baz bar)
>> +
>> +    (define-syntax foo?
>> +      (syntax-rules (foo)
>> +        ((_ foo) #t)
>> +        ((_ _) #f)))
>> +
>> +    (test-assert (foo? foo))
>> +    (test-assert (foo? bar))
>> +    (test-not (foo? baz)))
>> +
>> +      (test-group "standard auxiliary syntax"
>> +    (define-keyword otherwise else)
>> +    (test-assert (cond
>> +              (otherwise #t))))
>> +
>> +      (test-end))))
>> diff --git a/lib/chibi/keyword.scm b/lib/chibi/keyword.scm
>> new file mode 100644
>> index 00000000..fb45ac3d
>> --- /dev/null
>> +++ b/lib/chibi/keyword.scm
>> @@ -0,0 +1,37 @@
>> +(define keywords (make-hash-table eq?))
>> +
>> +(define (set-keyword! name)
>> +  (hash-table-set! keywords name (env-cell (current-environment) name)))
>> +
>> +;; Intern the keywords defined in (chibi).
>> +(set-keyword! '_)
>> +(set-keyword! '=>)
>> +(set-keyword! '...)
>> +(set-keyword! 'else)
>> +(set-keyword! 'unquote)
>> +(set-keyword! 'unquote-splicing)
>> +
>> +(define (hash-table-intern! ht key failure)
>> +  (hash-table-ref ht key (lambda ()
>> +                           (let ((res (failure)))
>> +                             (hash-table-set! ht key res)
>> +                             res))))
>> +
>> +(define (intern-keyword! name mac-env)
>> +  (hash-table-intern! keywords name
>> +              (lambda ()
>> +            (cons
>> +             name
>> +             (make-macro
>> +              (lambda (expr use-env mac-env)
>> +                (error "invalid use of auxiliary syntax"
>> +                   name))
>> +              mac-env)))))
>> +
>> +(%define-syntax define-keyword
>> +  (lambda (expr use-env mac-env)
>> +    (let ((_begin (make-syntactic-closure mac-env '() 'begin))
>> +      (id (cadr expr))
>> +      (name (strip-syntactic-closures (car (cddr expr)))))
>> +      (env-push-rename! use-env id (intern-keyword! name mac-env))
>> +      `(,_begin))))
>> diff --git a/lib/chibi/keyword.sld b/lib/chibi/keyword.sld
>> new file mode 100644
>> index 00000000..26434fbb
>> --- /dev/null
>> +++ b/lib/chibi/keyword.sld
>> @@ -0,0 +1,6 @@
>> +(define-library (chibi keyword)
>> +  (export define-keyword)
>> +  (import (chibi)
>> +      (chibi ast)
>> +      (srfi 69))
>> +  (include "keyword.scm"))
>> diff --git a/tests/lib-tests.scm b/tests/lib-tests.scm
>> index 8a200931..035751ab 100644
>> --- a/tests/lib-tests.scm
>> +++ b/tests/lib-tests.scm
>> @@ -46,6 +46,7 @@
>>          (rename (chibi io-test) (run-tests run-io-tests))
>>          (rename (chibi iset-test) (run-tests run-iset-tests))
>>          (rename (chibi json-test) (run-tests run-json-tests))
>> +    (rename (chibi keyword-test) (run-tests run-keyword-tests))
>>          (rename (chibi log-test) (run-tests run-log-tests))
>>          (rename (chibi loop-test) (run-tests run-loop-tests))
>>          (rename (chibi match-test) (run-tests run-match-tests))
>> @@ -111,6 +112,7 @@
>>  (run-io-tests)
>>  (run-iset-tests)
>>  (run-json-tests)
>> +(run-keyword-tests)
>>  (run-log-tests)
>>  (run-loop-tests)
>>  (run-match-tests)