Import modules properly
Haskell has a lot of variants of importing identifiers from other modules. However not all of them are as comfortable as they seem to be at the first glance. We recommend to focus on the following two forms of import:
import qualified Very.Special.Module as VSM import Another.Important.Module (printf)
import Very.Special.Module import Another.Important.Module hiding (open, close)
If you read
VSM.open in the program you can find out easily where the identifier comes from.
In the second case you don't know if these identifiers are from
Another.Important.Module or even other modules.
Mind you that grep won't help, because
Another.Important.Module might just re-export other modules.
In the second case, if new identifiers are added to the imported modules they might clash with names of other modules.
Thus updating imported modules may break your code.
It may also be that
Another.Important.Module.open was deprecated when you hid it,
and with a module update removing that identifier, your import fails.
That is, an identifier that you never needed but only annoyed you, annoys you again, when it was meant to not bother you any longer!
The first variant of import does not suffer from these problems.
I once found a bug in the StorableVector package by converting anonymous imports to explicit imports.
I found out that the function
Foreign.Ptr.plusPtr was imported,
although functions from this module always have to calcuate with unit "element" not "byte".
advancePtr must be used instead.
reverse function used
plusPtr and this was wrong.
A misbehaviour could only be observed for sub-vectors and elements with size greater than 1 byte.
The test suite did miss that.