[GHC] #14663: Deriving Typeable for enumerations seems expensive

[GHC]

#14663: Deriving Typeable for enumerations seems expensive
-------------------------------------+-------------------------------------
        Reporter:  niteria           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  low               |            Milestone:
       Component:  Compiler          |              Version:
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by simonpj):

 >  It appears that by default I pay >50% of compile time for a feature
 that I probably won't use.

 Yes, we debated this quite a bit.  For each data type we generate a bit of
 static information, just Haskell data structures, to describe the type.
 That way, anyone (in another module) who needs `Typeable T` or `Typeable
 'A0001` can have it.

 But mostly they don't need that, so it's wasted bloat.

 Another alternative is to generate those data structure on-the-fly in
 every client module.   Before long we'd be saying "let's avoid doing that
 multiple times in the same module, or doing it in module M if it's already
 done in one of M's imports", and we'd add machinery to avoid duplication.
 That is all extra complexity.  Maybe it's justified.  It'd be interesting
 to know who else tripped over this.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14663#comment:1>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler