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bug#23486: 25.0.93; Modules: features missing from make_function


From: Philipp Stephani
Subject: bug#23486: 25.0.93; Modules: features missing from make_function
Date: Sun, 26 Mar 2017 20:02:08 +0000



<address@hidden> schrieb am So., 11. Sep. 2016 um 16:56 Uhr:
Philipp Stephani <address@hidden> writes:

> emacs_env::make_function lacks the following features supported by
> `defun':
>
> 1. Functions with both optional and rest arguments.
> 2. Specification of parameter names.
> 3. Integration with `help-function-arglist'.
> 4. Specification of interactive forms.
> 5. Specification of declare forms.
> 6. Docstrings containing null or non-Unicode characters.
>
> (6) is probably rather unimportant.  (5) is probably not implementable
> (would require wrapping `defun', not `lambda').  (1)–(4) are more severe
> and quite limit the usefulness of make_function right now; for a
> truly generic `defun'-like construct one currently has to eval a `defun'
> form wrapping another function.

Shouldn't modules be providing a DEFUN-like construct instead?  That is,
I thought the idea of modules was to enable writing primitive
subroutines.

I don't know what the idea of modules originally was. However, defun and DEFUN are composite operations: They create a function object (lambda) and provide an alias for it. Therefore they can't replace the more primitive operations. The current module interface design chooses to provide the primitive operation to make a function object and have the caller call defalias. That's a reasonable choice.
 

>
> To solve (1)–(3), I'd propose replacing the "arity" arguments with a
> true arglist specification.  This could either be at the C level, e.g.
>
>     ptrdiff_t num_mandatory_args, char** mandatory_arg_names,
>     ptrdiff_t num_optional_args, char** optional_arg_names,
>     char* rest_arg_name
>
> or by requiring to pass a Lisp argument list.
>
> To solve (4) I'd propose to pass another value for the interactive form,
> probably as emacs_value* (to support non-interactive functions).
>
> As an alternative, if people feel this would require too many
> parameters, I'd propose reverting the change that adds the documentation
> string.  A docstring without arglist is not very useful.  We could also
> remove the arity parameters and have the C function check the arity
> itself.

I think adding "(fn ARG1 ARG2...)" to the docstring would solve (1)-(3).

That doesn't work, because Emacs ignores this syntax when the arguments are provided explicitly, and since a module function is just a (lambda (&rest args) ...) under the hood, the arglist is always just (&rest args).
 
What's lacking is a way to add this automagically like DEFUN does.  And
getting the parameters in C variables like DEFUN would also be nice.

Maybe, but not for the module interface. The module interface explicitly only provides basic primitives, without macro magic or high-level functions. High-level functionality built on top of the primitives is out of scope. 

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