[Haskell-cafe] Minimizing cascading rebuilds

[Brandon Allbery]

Optimizations shouldn't matter here: the problems there are caused by
inlining, and if this data were short enough to get inlined then it also
wouldn't be causing problems.

Although I should note that ByteString "literals" aren't actually literals
in the way the OP thinks, and this will also cause problems. The external
data file is actually preferable for this reason.

On Thu, Mar 29, 2018 at 1:25 AM, Dan Burton <danburton.email at gmail.com>
wrote:

> I don't believe this is currently possible with ghc, due to the way ghc
> handles optimizations. I would love to be proven wrong on that.
>
> On Wed, Mar 28, 2018, 22:11 ☂Josh Chia (謝任中) <joshchia at gmail.com> wrote:
>
>> Hi,
>>
>> In my project, I have multiple packages. One of the packages, packageA,
>> is very fundamental and depended on directly and indirectly by almost all
>> the other packages. It has functions that use some hard-coded data (a
>> ByteString top-level variable) also defined within packageA.
>>
>> This hard-coded data is appended regularly, causing packageA to be
>> rebuilt and thus almost all the other packages to be rebuilt, and building
>> takes a painfully long time. I know I can move this hard-coded data to a
>> file that's read at run-time, but that means one more item to plumb in at
>> run-time (where to find the file), and IO (preventing the functions from
>> being pure), so I would like to keep it hard-coded.
>>
>> Is there an elegant way to prevent or minimize the cascading rebuild of
>> the dependent packages just because the hard-coded data in packageA changed?
>>
>> For analogy, in C or C++, source code gets compiled to .o files, one for
>> each .cpp source file. Multiple .o files get linked into executables. So,
>> unless the interface (.hpp files) also change, an implementation (.cpp
>> file) change does not cause dependents to be recompiled to get new .o
>> files, although dependent executables get relinked. I'm not familiar with
>> the compilation and linking logic in GHC so maybe it has additional
>> complications.
>>
>> BTW, I'm using stack, in case it makes any difference to the nature of
>> the problem.
>>
>> Josh
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>
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-- 
brandon s allbery kf8nh                               sine nomine associates
allbery.b at gmail.com                                  ballbery at sinenomine.net
unix, openafs, kerberos, infrastructure, xmonad        http://sinenomine.net
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