[plt-dev] New forms for requiring files -- poll for opinions and names

From: YC (yinso.chen at gmail.com)
Date: Sun Oct 4 05:00:24 EDT 2009

So is the requirement to read a list of symbols from a config file and use
them as the mapping to the underlying modules?

Correct me if I am wrong, but doesn't planet already solve this problem?  It
helps define packages which are referred via symbols.  The changes to files
are localized within the package, and if you have a main.ss that require and
provide the underlying modules, it acts as the config.ss for other modules
requiring the package.  Versioning and network download/install are built-in
as well.

And cce/system/planet appears to solve the self referencing problem within a
single package -

The only thing lacking is that there are no private planet repositories for

Perhaps I misunderstood the goal here - please let me know if I missed


On Sat, Oct 3, 2009 at 1:15 PM, Eli Barzilay <eli at barzilay.org> wrote:

> An issue that came up recently with David -- and one that comes up
> every once in a while, is that of some project management tools.  A
> summary of the problem is: you have some layout of files in your
> project, and you want to be able to access them using in some symbolic
> way.  Using strings as relative names works to a limited degree: it
> means that the hierarchy is inflexible -- changing it requires
> changing files too.  Also, the paths depend on both the requiring
> module and the required one, usually you'll need a number of "../"s
> that depends on the requiring file, and a then the path of the
> required file.
> Now that we have require/provide forms, it is possible to solve this
> problem, and in typed-scheme Sam did something very similar to that,
> which makes it a nice use case.  Here's an example from one of Sam's
> files:
>  (require (except-in "../utils/utils.ss" extend))
>  (require (types convenience utils union subtype)
>           (rep type-rep)
>           (utils tc-utils)
>           "signatures.ss" "constraint-structs.ss"
>           scheme/match)
> When this came up with David, I pointed at all the obvious places that
> can be used to make it work, and then I continued to see if I can come
> up with some way to provide more convenient ways to dealing with such
> issues.  What I came up with is two require forms that I think would
> do this job nicely:
> * (file-in <expr>) -- this is close to `file', except that <expr> is
>  an arbitrary expression (evaluated at the syntax phase, of course).
>  It is similar to `filtered-in' (and uses the same
>  `scheme/private/at-syntax' hack) in that you write some code.  Using
>  the typed scheme snip as an example -- it would make writing those
>  `types' and `rep' forms easy.  (With a minor point: as they are in
>  this example, they would need to be macros, since their arguments
>  are not quoted.)
>  Also, it would be possible to have functions that consult some
>  "configuration file" which defines the project layout (with the
>  trivial case of the configuration file being some scheme module that
>  is required for-syntax), require files relative to your home
>  directory, the contents of an environment variable, the desktop
>  directory, etc, and it could even do some cheap networking thing
>  like downloading a file and then requiring it.
>  In other words, it does a job similar to Sam's `define-requirer',
>  except that it does so more generally, since you're using functions.
>  It's a little more verbose since you need the `file-in' wrapper --
>  but the advantage is that plain code is easier to write and would be
>  readable to more people.  (For example, if you're looking at some
>  random file in typed scheme, you won't know what it's supposed to
>  do.)
> This solves one side of the problem -- organizing code with such a
> symbolic approach is becoming much easier.  But the other side of this
> problem is that you'd want to centralize such code, and you need to
> reach that central point conveniently from everywhere in your project.
> Going back to the typed scheme snippet, this is the
> "../utils/utils.ss" part.  This string still depends on the location
> of the central configuration file wrt the project root.  I'm not sure
> what would be the best solution -- the best thing I can think of is:
> * (file-up <string>) -- searches for a path in this directory, then
>  going up.  If there was some `or-in' form, then (file-up "foo/z.ss")
>  this would be similar to:
>    (or-in "foo/z.ss" "../foo/z.ss" "../../foo/z.ss" ...etc...)
>  With this, Sam's code could use (file-up "utils/utils.ss").
> Combining these two, and assuming that they're provided by
> `scheme/require', a typical "project management" code chunk could look
> like:
>  (require scheme/require
>           (file-up "config.ss")
>           (file-in the-foo-utility
>                    (subsystem1 'blah)
>                    (subsystem2 'sheep/goes/meh)))
> where the "config.ss" file provides (for syntax) the definitions for
> the subsystem functions and the first value.  (One tricky bit: the
> order of the three require clauses is important.)
> One point that Matthew raised when I talked to him about this is that
> it can lead to a mess if the functions that you're using in `file-in'
> are non-deterministic.  This problem is already in now, of course, the
> only thing that changes is how easy you can get to it.  But given the
> utility of these forms (in contexts that make this pop up every once
> in a while), I think it should generally be fine -- as long as the
> documentation has the right warnings, as well as some boilerplate code
> that most people will just copy and modify.
> So, are there any opinions on this?  Or on the specific forms?
> Also, I'm not sure about the names.  The `file-in' vs `file' (vs
> `file-up') seems like it can be confusing, so maybe `path-in' and
> `path-up' would work better?  Another alternative is to have a
> *function* that does the up-search, and provide it for syntax, with a
> use-case like:
>  (require scheme/require
>           (file-in (look-up "config.ss"))
>           (file-in the-foo-utility
>                    (subsystem1 'blah)
>                    (subsystem2 'sheep/goes/meh)))
> but this seems like it can be much more confusing.  Another option is
> some `file-in-up' which combines the two features (expects an
> expression, and does the search with the result) -- this seems to me
> like cramping too much functionality into a single tool.
> Yet another option is have `file-in' be some `#%app'-like thing, so
> the above code becomes:
>  (require scheme/require
>           (file-up "config.ss")
>           (file-in the-foo-utility)
>           (file-in subsystem1 'blah)
>           (file-in subsystem2 'sheep/goes/meh))
> --
>          ((lambda (x) (x x)) (lambda (x) (x x)))          Eli Barzilay:
>                    http://barzilay.org/                   Maze is Life!
> _________________________________________________
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>  http://list.cs.brown.edu/mailman/listinfo/plt-dev
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