I wanted to build HDBC-postgresql 1.0.1[1] today, and ran into a problem where my test program would not load and instead gave this error:

  can't load .so/.DLL for: pq (addDLL: unknown error)

I traced this to the 'extra-libraries' directive in the .cabal file. It read

Extra-Libraries: pq

When I changed it to

Extra-Libraries: libpq

The error went away. Somehow "pq" is not enough to get "libpq.dll" loaded.

Note that building on Windows required some other changes.[2]

This was using Cabal 1.1

[1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HDBC-postgresql-1.0.1.0

[2] From http://software.complete.org/hdbc/wiki/FrequentlyAskedQuestions

To build on Windows, you must specify where the postgresql include and library files are. Follow these two steps:

1. Ensure the files are NOT installed in a directory with spaces in the name (e.g. "C:\Program Files"). For example, install them in c:\pgsql.
2. Assuming postgresql is installed in C:\pgsql, add the following information to the .cabal file:

      include-dirs: C:\pgsql\include, C:\pgsql\include\server, .
      extra-lib-dirs: C:\pgsql\bin

Notice the "." at the end of include-dirs to ensure the current directory is also searched. Also notice "bin" directory is specified in "extra-lib-dirs." This is important in the next step.

1. HDBC-postgresl depends on "libpa.dll" in the bin directory above. The .cabal file refers to the "pq", but that doesn't work on Windows. Change it to libpq like so:

Extra-Libraries: libpq

Trac metadata

Trac field	Value
Version	6.6.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture