Commit a8bf3684 authored by sewardj's avatar sewardj
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[project @ 1999-12-16 16:42:56 by sewardj]

Add extended version of previous commit message as a comment.
parent 0c97d649
......@@ -7,8 +7,8 @@
* Hugs version 1.4, December 1997
*
* $RCSfile: interface.c,v $
* $Revision: 1.11 $
* $Date: 1999/12/16 16:34:40 $
* $Revision: 1.12 $
* $Date: 1999/12/16 16:42:56 $
* ------------------------------------------------------------------------*/
/* ToDo:
......@@ -40,6 +40,7 @@
extern void print ( Cell, Int );
/* --------------------------------------------------------------------------
* (This comment is now out of date. JRS, 991216).
* The "addGHC*" functions act as "impedence matchers" between GHC
* interface files and Hugs. Their main job is to convert abstract
* syntax trees into Hugs' internal representations.
......@@ -70,6 +71,65 @@ extern void print ( Cell, Int );
*
* ------------------------------------------------------------------------*/
/*
New comment, 991216, explaining roughly how it all works.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Interfaces can contain references to unboxed types, and these need to
be handled carefully. The following is a summary of how the interface
loader now works. It is applied to groups of interfaces simultaneously,
viz, the entire Prelude at once:
0. Parse interfaces, chasing imports until a complete
strongly-connected-component of ifaces has been parsed.
All interfaces in this scc are processed together, in
steps 1 .. 8 below.
1. Throw away any entity not mentioned in the export lists.
2. Delete type (not data or newtype) definitions which refer to
unknown types in their right hand sides. Because Hugs doesn't
know of any unboxed types, this has the side effect of removing
all type defns referring to unboxed types. Repeat step 2 until
a fixed point is reached.
3. Make abstract all data/newtype defns which refer to an unknown
type. eg, data Word = MkW Word# becomes data Word, because
Word# is unknown. Hugs is happy to know about abstract boxed
Words, but not about Word#s.
4. Step 2 could delete types referred to by values, instances and
classes. So filter all entities, and delete those referring to
unknown types _or_ classes. This could cause other entities
to become invalid, so iterate step 4 to a fixed point.
After step 4, the interfaces no longer contain anything
unpalatable to Hugs.
5. Steps 1-4 operate purely on the iface syntax trees. We now start
creating symbol table entries. First, create a module table
entry for each interface, and locate and read in the corresponding
object file. This is done by the startGHCModule function.
6. Traverse all interfaces. For each entity, create an entry in
the name, tycon, class or instance table, and fill in relevant
fields, but do not attempt to link tycon/class/instance/name uses
to their symbol table entries. This is done by the startGHC*
functions.
7. Revisit all symbol table entries created in step 6. We should
now be able to replace all references to tycons/classes/instances/
names with the relevant symbol table entries. This is done by
the finishGHC* functions.
8. Traverse all interfaces. For each iface, examine the export lists
and use it to build export lists in the module table. Do the
implicit 'import Prelude' thing if necessary. Finally, resolve
references in the object code for this module. This is done
by the finishGHCModule function.
*/
/* --------------------------------------------------------------------------
* local function prototypes:
* ------------------------------------------------------------------------*/
......
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