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  1. Oct 25, 2014
  3. Oct 24, 2014
    • Edward Z. Yang's avatar
      Implementation of hsig (module signatures), per #9252 · aa479953
      Edward Z. Yang authored 
      
Summary:
Module signatures, like hs-boot files, are Haskell modules which omit
value definitions and contain only signatures.  This patchset implements
one particular aspect of module signature, namely compiling them against
a concrete implementation.  It works like this: when we compile an hsig
file, we must be told (via the -sig-of flag) what module this signature
is implementing.  The signature is compiled into an interface file which
reexports precisely the entities mentioned in the signature file.  We also
verify that the interface is compatible with the implementation.

This feature is useful in a few situations:

    1. Like explicit import lists, signatures can be used to reduce
    sensitivity to upstream changes.  However, a signature can be defined
    once and then reused by many modules.

    2. Signatures can be used to quickly check if a new upstream version
    is compatible, by typechecking just the signatures and not the actual
    modules.

    3. A signature can be used to mediate separate modular development,
    where the signature is used as a placeholder for functionality which
    is loaded in later.  (This is only half useful at the moment, since
    typechecking against signatures without implementations is not implemented
    in this patchset.)

Unlike hs-boot files, hsig files impose no performance overhead.

This patchset punts on the type class instances (and type families) problem:
instances simply leak from the implementation to the signature.  You can
explicitly specify what instances you expect to have, and those will be checked,
but you may get more instances than you asked for.  Our eventual plan is
to allow hiding instances, but to consider all transitively reachable instances
when considering overlap and soundness.

ToDo: signature merging: when a module is provided by multiple signatures
for the same base implementation, we should not consider this ambiguous.

ToDo: at the moment, signatures do not constitute use-sites, so if you
write a signature for a deprecated function, you won't get a warning
when you compile the signature.

Future work: The ability to feed in shaping information so that we can take
advantage of more type equalities than might be immediately evident.

Signed-off-by: default avatarEdward Z. Yang <ezyang@cs.stanford.edu>

Test Plan: validate and new tests

Reviewers: simonpj, simonmar, hvr, austin

Subscribers: simonmar, relrod, ezyang, carter, goldfire

Differential Revision: https://phabricator.haskell.org/D130

GHC Trac Issues: #9252
      aa479953
    • Edward Z. Yang's avatar
      Check in up-to-date PDF copies of Backpack docs. [skip ci] · 5bb73d79
      Edward Z. Yang authored 
      
Signed-off-by: default avatarEdward Z. Yang <ezyang@cs.stanford.edu>
      5bb73d79
    • Edward Z. Yang's avatar
      More updates to Backpack manual [skip ci] · 427925d0
      Edward Z. Yang authored 
      
Signed-off-by: default avatarEdward Z. Yang <ezyang@cs.stanford.edu>
      427925d0
  5. Oct 23, 2014
    • Simon Marlow's avatar
      Fix a rare parallel GC bug · a11f71ef
      Simon Marlow authored 
      When there's a conflict between two threads evacuating the same TSO,
in some cases we would update the incall->tso pointer to point to the
wrong copy of the TSO.  This would get fixed during the next GC, but
if the thread completed in the meantime, it would likely crash.  We're
seeing this about once per day on a heavily loaded machine (it varies
a lot though).
      a11f71ef
  7. Oct 22, 2014
  9. Oct 21, 2014