GHC-6.4.1 much slower than GHC-6.4

[Christian Maeder]

Hi,

I've found a way to speed up your code for ghc-6.4.1.
Replace the "where" with a "case" in PCP.Suc.suc_rules (see below)
(Maybe that is a good idea in PCP.Rules.Suc, too)

I don't know why this can be better optimized, but my profiling results 
are comparable to those of ghc-6.4 (without the change).

Cheers Christian

  suc_rules sigma vp rs         =  case PCP.Rules.suc sigma rs of
     sucr ->  \ conf -> do
				 f <- sucr conf
				 guard $ valid vp f
				 return f

	total time  =      251.22 secs   (12561 ticks @ 20 ms)
	total alloc = 15,875,706,252 bytes  (excludes profiling overheads)

COST CENTRE                    MODULE               %time %alloc

transF                         NFA.Type              14.7    1.1
steps                          Util.Graph.BFS         6.2    2.2
trans_manyF                    NFA.Type               6.2    9.9
dfs_collect                    Util.Graph.DFS         5.0    4.0
step                           Util.Graph.BFS         4.2    0.6
build                          PCP.Rules.Excl.Type    2.9    3.6
isPartOf                       Util.Words             2.8    5.8
lang_ok                        PCP.Rules.Type         2.7    5.0
intersect                      NFA.Intersect          2.7    6.1
dfs_abort                      Util.Graph.DFS         2.5    2.4
transF                         NFA.DFA.Type           2.2    1.4
meet                           PCP.Search             2.1    0.6
det_tqf                        NFA.Det                1.8    3.3
genericCross                   Util.Cross             1.7    4.3
productive                     NFA.Intersect          1.6    3.5
det_dfa                        NFA.Det                1.5    1.1
build                          NFA.DFA.Hopcroft       1.5    3.1
subset                         NFA.Subset             1.4    2.2
apply                          PCP.Rules.Rule         1.4    2.6
map_fun                        Util.Map               1.3    1.2
complement                     NFA.Det                1.3    0.7
apply                          PCP.Rules.Type         1.1    1.5
suc                            PCP.Rules.Suc          1.0    1.0
ok                             PCP.Util.OK            1.0    0.6
select                         PCP.Rules.Type         1.0    1.4
is_final                       NFA.Type               0.7    1.0
sublistsN                      Util.Words             0.5    1.2
num_rules                      PCP.Rules.Type         0.4    1.0