─ cabal install haskelldb-hdbc-postgresql       

Resolving dependencies...
In order, the following would be installed:
convertible-1.0.11.1 (new package)
HDBC-2.3.1.2 (new package)
HDBC-postgresql-2.3.2.1 (new package)
haskelldb-2.2.2 (reinstall) changes: mtl-2.0.1.0 -> 2.1.1
haskelldb-hdbc-2.2.2 (new package)
haskelldb-hdbc-postgresql-2.1.2 (new package)
cabal: The following packages are likely to be broken by the reinstalls:
haskelldb-th-2.1.0
Use --force-reinstalls if you want to install anyway.

cabal install --force-reinstalls haskelldb-hdbc-postgresql
...
Installed haskelldb-hdbc-postgresql-2.1.2

─ cabal install haskelldb-th  
                                                        
Resolving dependencies...
In order, the following would be installed:
haskelldb-2.2.2 (reinstall) changes: mtl-2.1.1 -> 2.0.1.0
haskelldb-th-2.1.0 (reinstall) changes: haskelldb-2.2.2 added
cabal: The following packages are likely to be broken by the reinstalls:
haskelldb-hdbc-postgresql-2.1.2
haskelldb-hdbc-2.2.2
Use --force-reinstalls if you want to install anyway.

Adrian.