Question

In Python, I can run a bit of code optionally if a given package exists like so:

try:
  import asd
  # do something with asd
except ImportError:
  print "no module asd"

Is there a Haskell equivalent?

Answer 1

Not directly, since module imports are resolved at compile-time with GHC. But if you’re using Cabal (and you should be!), you can conditionally depend on a package according to a configuration flag, and then use the CPP extension to compile code depending on whether or not that dependency is present:

#if MIN_VERSION_somepackage(0,0,0)
...code using somepackage...
#else
...code not using somepackage...
#endif

This is kind of awkward, though, so I wouldn’t recommend using it unless you really need it…