recompilation check in 6.4

Serge D. Mechveliani mechvel at
Sun Jun 5 06:58:17 EDT 2005

People, who knows, please, how to fix re-compilation in ghc-6.4
Porting my program  dm  from  6.2.2  to  6.4, 
I see that the 6.4 system re-compiles many modules when 
re-processing the Makefile to build  dm.
For example, let  Foo.hs  from  dm  contain an error  
"value  v  not in scope".
Running                   make dm 

for the first time compiles all the modules before  Foo  in  
50 seconds.
Then, I fix an error in  Foo.hs  and repeat  "make dm".

The  options are set so  that  ghc-6.2.2  gets to  Foo.hs  in less 
than 1 second when doing this repeated `make'.  
It does consider each module before Foo and each time decides that 
there is no need in recompilation. It keeps on going this way:
Considering whether compilation is required for Prelude0:
Skipping  Prelude0  ( ./Prelude0.hs, /foo/source/export/Prelude0.o )
and so on, by the scheme
"Considering ..XX -- {Checking usages .. --} Skipping XX". 

The compiler applies this way: 
/foo/ghc/6.2.2/inst/bin/ghc  -fglasgow-exts  
-fallow-overlapping-instances -fno-warn-overlapping-patterns  
-fwarn-unused-binds -fwarn-unused-matches  -fwarn-unused-imports  
-odir /home/mechvel/dm/1.02/dm/source/export 
-hidir /home/mechvel/dm/1.02/dm/source/export 
--make DExport  -package-name dm

Now, when  ghc-6.4  does such a repeated `make', it re-compiles 
all the `previous' modules under the above options:
Chasing modules from: DExport
    Source file changed or recompilation check turned off
Compiling Prelude0     ( ./Prelude0.hs, /.../source/export/Prelude0.o )
Interface file unchanged

(And when setting to  Foo  a _syntax_ error, 6.4 finds this error
without compiling `previous' modules).

Something has changed in 6.4, maybe, the default for the recompilation 
check, I do not know.
6.2.2 did what was intended in Makefile.

Who knows, please, how to fix this recompilation point in 6.4 ?

Thank you in advance for explanation.

Serge Mechveliani
mechvel at

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