TODO

								     -*-text-*-
                                C2HS TODO
                                =========

Next: - enum hooks should define cFromEnum/cToEnum as the default marshallers
       (see comment at GenBind.lookupDftMarshIn).

      - Especially with function hooks, it is not sufficient to emit line
	pragmas whenever a new CHS fragment starts.  As some hooks expand to
	multiple lines of Haskell code, we need to reemit the line number of
	the hook once for each line of Haskell generated from it.

      - Points raised by PeteG:
	* The initial comment put by c2hs shouldn't be put in the first line,
	  as this makes it difficult to add {-# OPTIONS #-} pragma to the .chs
	  file, as this pragma must be in the first line.

          The only sensible solution seems to be to copy the first line of the
          .chs file on top if it starts with the string "{-# OPTIONS".

      - Ian requests {#const SYM#} where SYM is a pre-preprocessor symbol to 
        evaluate to the C value of SYM.  Main problem is that the value might
        be of various C types.

      - Tutorial

      - GenBind.setGet: How is it justified that `bitsPerField' is
        fixed to the size of `CInt'?  Does the C def guarantee
	that bitfields types are of the same size?

      Next Major feature to be added: structure marshalling.

      - the `hsverb' should be normalised with respect to white space and
        parenthesis 

      - have an option to compute .chi dependencies; do this on a
        module-by-module basis generating many small depend files rather than
        one big one

      - Pending suggestions from Axel Simon:
	+ succ/pred definitions for enum hooks

      - marshalling of structs

      - We need to handle the time stamps of .chi files more carefully;
        otherwise, we often get lots of unnecessary re-runs of c2hs.

      - Conceptual problem with import hooks: Currently, everything imported
        from a .chi file by a binding module is also dumped into its own .chi
        file.  Is is not generally correct, but it would also not be correct
        to omit everything that has been imported.  The conceptually correct
        solution would be to dump an entry for a type into a .chi file if the
        corresponding Haskell type is exported by the binding module.  To
        achieve this, we would also need an export hook.  Moreover, we may
        import the same object from different modules, due to an implicit
        reexport at the moment.  Either eliminate those reexports, or we have
        the same problems as in Haskell to determine object identity.

      - c2hs has to properly process GNU C "aligned" attributes.  Otherwise,
        it's routine to calculate structure layout may deviate from that of
        the C compiler, which may lead to nasty bugs in bindings.

      - the use of get/set hooks with `class'ed newtypes is complicated, as
        the type doesn't match `Ptr a'; see, e.g. `GtkCList.cListGetNoOfRows'

      - class methods should be able to get user-defined names (needed for
        GtkData.chs)

      - GenBind.mergePtrMap could be improved (see the comment)

      - {#enum ...#} should create an instance of Storable as follows:
	  instance Storable MyEnum where
	    sizeOf    _ = sizeOf    (undefined :: CInt)
	    alignment _ = alignment (undefined :: CInt)

	    peek p   = liftM cToEnum $ peek (castPtr p :: Ptr CInt)
	    poke p v = poke (castPtr p :: Ptr CInt) (cFromEnum v)

      - `GenBind.setGet' needs to take `C2HSConfig.bitfieldDirection' into
        account; otherwise, setting and getting of bitfields won't work on
        architectures where bitfields start at the MSB (rather than the LSB)

      - Vorschlag von Axel Krauth <krauth@infosun.fmi.uni-passau.de>:
        An option with which c2hs prints a list of all functions that have not
        been bound in a header file.  The Position info schould be sufficient
        to determine this.  Maybe also add {#ignore foo#}, which makes it not
        list a given identifier (for private functions listed in the header).
      - In `GdkGL.chs', the prefix is not properly removed from the
        constructors of `GdkGL.Configs'; same problem with
        `GdkEvents.EventType'
      - install the executable (c2hs and c2hs-config) with a version number
        suffix and make a symbolic link for the name without version number
        (makes installing multiple versions easier)
      - #define enum's (see below)
      - intro a safe flag (as opposite to unsafe, but make safe the default)
      - overload stdAddr etc for ForeignObj (stable ptr & cast)
      - C2HSMarsh: from qrczak@knm.org.pl (Marcin 'Qrczak' Kowalczyk)
	  mallocForeignObj:: Int -> IO ForeignObj     -- malloc + freeing finalizer
      - C2HSMarsh: 
	  (!!!)   :: FromAddr a => Ptr a -> Int -> IO a
	  p !!! i  = do
		       v <- fixIO $ deref (p `plusAddr` sizeof v * i)
		       return v
          (Use in GdkColor, then)
	  Part of New FFI, so use that in GdkColor!
      - C2HSMarhs:
	for compound structures it is inconvenient that in a pointer-based
        out, an initial value is needed; thus
	  out   :: (Storable a, FromAddr a) => a -> Marsh a Addr
	  out x  = malloc x :> addrStd
	and this is also convenient
	  inp   :: ToAddr a => a -> Marsh () Addr
	  inp x  = stdAddr x :> free
        Axel also proposes this
	  byValue :: b -> Marsh () b
	  byValue x = use x :> forget
      - Axel suggests,
	  2b. Automatisches Marshalling von Strukturen.
	  Eigentlich müßte es doch möglich sein, automatisch Instanzen von
	  Storable für Strukturen zu erstellen. Falls man mal einen generische
	  Pointer hat, kann man ja mit der ... as ... Methode eigene
	  Marshalling Funktionen zur Verfügung stellen. Oder habe ich da etwas
	  grundsätzliches übersehen? 

Short term
~~~~~~~~~~
* cpp directives on the very first line of the .chs file are ignored
  because the lexer looks for \n#  This is very confusing to users.

* The C99 spec says (sec. 6.7.2.1):

       [#4] Each  enumerated  type  shall  be  compatible  with  an
       integer     type.      The     choice     of     type     is
       implementation-defined   but   shall   be   capable   of
       representing  the  values  of  all  the   members   of   the
       enumeration. [...]

  Hence, c2hs has to be a bit more clever about determining the integral type
  used to represent an enum.

* The definition of `GenBind.HsObjectMap' doesn't take into account that in
  Haskell a single name can be used for both a type and a class.

* See FIXME at `GenBind.mergeMaps'.

* Explain the grabbing of cpp -I options from -cppopts= (aka -C) values better 
  in the docu and add something like:

    I prefer that to giving an option to c2hs and passing it to
    cpp, because - as you say - you usually already have a
    variable with the cpp options in your makefile and this way
    you can easily reuse it.

* #define enums in C: siehe unten - scheinen aber wichtig

* In pointer hooks after a `->', we currently allow only type identifiers;
  other forms of Haskell types would be nice, too (especially, `()').

* A function prototype that uses a defined type on its left hand side may
  declare a function, while that is not obvious from the declaration itself
  (without also considering the `typedef').  This is not understood by
  `GenBind' so far.

* Why is a stable name an `unsigned long' in C land?  How about a `void *' and 
  being able to get the `Addr' also in Haskell land?

* if in a binding file erroneously `t->m' is used instead of `t.m' and `t' is
  the tag of a struct, the error message just complains that there is no type
  object for called `t'; it would be more user friendly to report in addition
  that the tag `t' exists, but cannot be used in this expression

* Should it be possible to specify a calling convention in context hook?
  Isn't it a mitake to have explicit calling convention in the FFI?  Shouldn't 
  that be adapted automatically depending on the target architecture?

* Sven: How about exporting Haskell functions (also dynamic export)?
  - callback registration function that explicitly have the type of the
    callback function (from which we might want to generate a foreign export
    dynamic). 

* `mapM raise errs' in `lexC' increases the heap usage by a factor of _8_ when 
  running the lexer alone on `gtkext.h' - probably because the whole analysis
  has to be completed before we can be sure to have no error (and this kills
  an interlocked produced/consumer scheme for the lexer and whatever function
  is consuming the tokens).

* sizeof and type hooks do only allow defined, but not basic types as
  arguments.  This is not a real problem as C2HS provides all the needed
  information to circumvent such usage, but it would still be more elegant to
  support basic types as arguments, too.

Middle term
~~~~~~~~~~~

* A hook {#const <C expr>#} would be nice (as in hsc2hs).  Unfortunately, it
  is not that easy to realise.  We need to parse the <C expr> in the binding
  module.  Moreover, the main value of this would be when the <C expr> is
  put into the C field together with `enum define' stuff, so that all
  pre-processor symbols in it are resolved.  However, this can easily give us
  C compiler errors.  A cheap way out would be {#const "C expr"#} to avoid
  parsing the C expression, but then we can get even more errors during
  compiling the C.

* C->HS might get a lot easier to use by providing as optional marshalling
  libraries modules that handle often occurring standard stuff like converting 
  `time_t' to `CalendarTime' or handle sockets etc.  We would, then, probably
  like to have a matching Posix or so library.

------------ Pre-1.0 rewrite ---------------

Problems:

* There are some implicit requirements on the position of binding hooks, which
  the tool doesn't really enforce: context must be first, context and enum may
  only occur where a toplevel definition is allowed. (This should be checked
  before `GenBind' is used.)  We can not really check that a hook is in a
  position where a toplevel definition is allowed (without analysing
  significant parts of the Haskell code), but we can at least guarantee that
  these hooks occur in column position 0.

* Sven: #define enums in C: Introduce (#enum define SomeEnum {...}#) hooks
  that collect `#define' symbols into an enumeration type; see also
  +haskell/4025.  One probem: If identifiers with the same lexeme as
  `SomeEnum' or the enum members are already defined in the C header, we might 
  get conflicts.

  The problem of this approach is that if the macro expands to something that
  is not a constant expression C, we will get error messages from the
  preprocessor, which are strange to the user.

  Further idea, Michael's: extensible enums

  There are, however, a number of interesting options supported by gcc -E that
  might make alternative solutions to the problem feasible.

END of ----- Pre-1.0 rewrite ---------------

* Do we like direct support for mapping complete structs (if they are
  sufficiently wellbehaved?) into Haskell data structures - both by generating
  the Haskell data type definitions and by generating a `cFrom<Struct>' and a
  `cTo<Struct>' routine.  The latter would be generated as a cascade of field
  hooks.  H/Direct's formal definition of structure marshalling might be
  helpful here.

* Support for evaluating constants is not complete yet.  In this context, it
  should probably also be checked, when there are two overlapping tags in an
  enum (this is allowed in C, but is problematic for marshaling). 

* How about Hugs support?  Is it already possible with current Hugs?


Release Checklist
~~~~~~~~~~~~~~~~~

(1) In root of working directory,

      % make tar-c2hs

(2) Compile the resulting source distribution with latest ghc stable release:

      % tar xzf c2hs-x.y.z.tar.gz
      % cd c2hs-x.y.z
      % ./configure
      % make

(3) Install and regression testing:

    - Installation procedure

        % make install

    - Tests in build/ghc?/c2hs/tests/ directory

(4) Check documentation and add release notes

(5) Extended build test: build with older stable release of ghc and with the
    cvs version

(6) Register CVS tags for CTK and C->HS (syntax: Release-c2hs_x_y_z)

(7) Make newest `tar' and build rpm

(8) Put tar.gz and rpm sources and binaries up on Web page

(9) Optionally also release the current version of CTK

(10) Update the documentation under the Web page's docu/ directory

(11) Announce: haskell@haskell.org, freshmeat.net