problems using ghc-6.6.1 (due to fgl-5.4.1)

Christian Maeder maeder at
Tue May 8 17:33:28 EDT 2007

I wrote:
> Dear Hets- and GHC-Developers,

> we have a problem using ghc-6.6.1. The created hets binary runs a
> couple
> of times slower than the one created using ghc-6.6.

This problem is gone when I install and use fgl-5.3 (where "hiding
(indices)" needs to be deleted in Data.Graph.Inductive.Monad.IOArray).

I strongly suspect the new functions context1l' and context4l' in
Data.Graph.Inductive.Graph (fgl-5.4.1) to be the reason for our drastic
slow down.

In fgl-5.3 the functions fst4 and fth4 have been used instead. A cyclic
edge (an edge from and to the very same node) was only returned as
ingoing edge and not as outgoing one. (a design decision documented

I think, the change in fgl-5.4.1 now returns a cyclic edge also as
outgoing edge (and possibly twice as ingoing one).

Our application heavily uses in- and outgoing edges that may be cyclic.


P.S. ghc-6.6.1/libraries/fgl/Setup.hs does not compile with ghc-6.6.1

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