hdevtools is a backend for text editor plugins, to allow for things such as
syntax and type checking of Haskell code, and retrieving type information, all
directly from within your text editor.
The advantage that
hdevtools has over competitors, is that it runs silently
in a persistent background process, and therefore is able to keeps all of your
Haskell modules and dependent libraries loaded in memory. This way, when you
change only a single source file, only it needs to be reloaded and rechecked,
instead of having to reload everything.
hdevtools very fast for checking syntax and type errors (runs just
as fast as the ':reload' command in GHCi).
In fact, syntax and type checking is so fast, that you can safely enable auto checking on every save. Even for huge projects, checking is nearly instant.
Once you start using
hdevtools and you get used to having your errors shown
to you instantly (without having to switch back and forth between GHCi and your
editor), and shown directly on your code, in your editor (without having to
wait forever for GHC to run) you will wonder how you ever lived without it.
In addition to checking Haskell source code for errors,
hdevtools has tools
for getting info about identifiers, and getting type information for snippets