#1409: Allow recursively dependent modules transparently (without .hs-boot or
anything)
---------------------------------+------------------------------------------
Reporter: Isaac Dupree | Owner:
Type: feature request | Status: new
Priority: normal | Milestone: _|_
Component: Compiler | Version: 6.10.2
Keywords: | Testcase:
Blockedby: | Difficulty: Unknown
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
---------------------------------+------------------------------------------
Comment(by simonpj):
Another thread has started on Haskell Cafe about this ticket. I thought
it worth jotting down how I'd approach implementing the feature.
If we wanted to support mutually recursive modules transparently, which is
a reasonable goal, then the Right Thing is surely to identify the
strongly-connected components and compile each SCC all together, as if it
were all in a single module.
From a design point of view, here are some thing to consider
* Doing so would make each SCC all or nothing. If you make a change to
any module, all get recompiled. With `hs-boot` files, the recompilation
checker is more discriminating.
* Would we expect to generate one `.o` and `.hi` file for the SCC, or one
for each original module? Currently lots of built-system and GHC-internal
stuff expects one-per-module. But that would mean splitting up the mixed-
together definitions after compilation. (Not as trivial as it sounds: we
might have done CSE across modules by that time.)
* What to do in "batch mode", when you say `ghc Foo.hs` without `--make`?
(To identify the SCC you need to do `--make`.)
* Since we already have the `hs-boot` we'd need to figure out how it
inter-operates with the new mehanism.
From an implementation point of view
* The main compilation pipeline would have to be taught about reading
several source files for one compilation run.
* GHC does not currently expect to be compiling definitions from several
modules at once. In principle there should be no difficulty here, but when
you break a long-standing assumption there are ''always'' difficulties.
Hard to know just what.
I think all of this is do-able. But it's a significant task.
Simon
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1409#comment:37>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
_______________________________________________
Glasgow-haskell-bugs mailing list
[email protected]
http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
