Re: [MLton] RFC: implement "use" function to support explicit file dependency

On Wed, Feb 05, 2014 at 10:16:21AM +1100, James Deng wrote:
> Here I propose to add implementation of the optional “use” function
> in the ML basis library, to support explicit file dependencies. To avoid
> problems, the string argument of “val use: string -> unit” can be
> restricted to compile-time constants.

I think this is reasonable, from the perspective of someone using the
compiler. It's portable and easy to understand.

But implementing it is not trivial. You'd have to go through the
stages of the compiler to get to the point where the "use" function is
understood to be a particular "use" primitive (I guess past FrontEnd,
which is not expensive), and then rerun all the stages you went through
to get there. But you'd probably want to get past at least XMLSimplify,
(after FrontEnd, Elaborate, and Defunctorize; pretty expensive), so you
could actually understand that the argument to "use" is a constant.

By that point, it's going to take a lot of time to rerun those stages
again. Every use of "use" is going to require going through everything
again, unless you could figure out how to splice a new file into the
internal representation you already have, which I'm not sure is possible.

So this would require a substantial reorganization of the compiler, and
I'm pretty sure it would always be very slow to compile any code using this.
It's really not in the spirit of a whole-program compiler.

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