Persistent GHC powered background server for FAST Haskell development tools
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
hdevtools is designed to be integrated into text editors. The list of current
editor plugins that supply this integration is below.
But before you do anything, you must first install
hdevtools itself. The
easiest way is from Hackage via cabal install:
$ cabal install hdevtools
Then you should install one or more of the following editor plugins:
Vim - Syntastic
Syntastic is a popular syntax checking plugin for Vim, and is the
recommended Vim integration of
hdevtools syntax and type checking. Recent
versions of Syntastic(since Sep. 2012) have builtin support for
hdevtools (as above) and Syntastic, and it will
automatically check your Haskell files.
Vim - vim-hdevtools
In addition to Syntastic, it is recommended that you also use
vim-hdevtools for additional functionality.
vim-hdevtools offers integration with the rest of the
including retrieving info about the identifier under the cursor, and getting
the type of the code under the cursor. Refer to its documentation for more
Emacs - flycheck
Most editors allow you to run a
make command, and will then parse the output
for errors and show line numbers, allowing you to jump between errors.
hdevtools check command is suitable for such usage.
For example, in Vim something like this will work:
:let &makeprg='hdevtools check %'
(Vim will replace the
% character with the name of the current file). Then
you can run
And Vim will invoke
hdevtools to check the current file for errors, and then
show a list of them and allow jumping to them.
See the "Command Line Usage" section below for more information.
Note: When using one of the above editor plugins, you don't really need to know this.
For the list of commands available, run:
$ hdevtools --help
To get help for a specific command, run:
$ hdevtools [COMMAND] --help
$ hdevtools check --help
The first time
hdevtools runs a command, it will spawn a background process
that will remain running forever. You can check the status of this background
process by running:
$ hdevtools --status
You can shutdown the background process by running:
$ hdevtools --stop-server
Communication with the background process is done through a unix socket file.
The default name is
.hdevtools.sock, in the current directory. This allows
you to use
hdevtools with multiple projects simultaneously, without the
background processes getting in the way of each other.
You can use a different socket file name with the
--socket option, which
should be used for each invocation of
hdevtools. Remember that when telling
hdevtools to check a Haskell file, paths are relative to the path of the
background process, not your current directory. This can cause problems, and
therefore it is recommended that you leave the socket file as the default, and
hdevtools from the same directory.
For most non-trivial projects, you will need to tell
additional GHC options that your project requires.
hdevtools commands accept a
-g flag for this purpose.
- Your project source code is in the directory
- You want to use the GHC option
- You want to hide the package
transformersto prevent conflicts
hdevtools with something like this:
$ hdevtools check -g -isrc -g -Wall -g -hide-package -g transformers Foo.hs
Notice that a
-g flag is inserted before each GHC option. Don't try to string
multiple GHC options together after a single
This won't work:
$ hdevtools check -g '-hide-package transformers' Foo.hs
The Vim plugins allow setting GHC options in the
variable. For example, for the above project, put the following in your
let g:hdevtools_options = '-g -isrc -g -Wall -g -hide-package -g transformers'
In general, you will need to pass to
hdevtools the same GHC options that you
would pass to GHCi.
hdevtools was inspired by ghcmod, but has the advantage that due to its
client-server architecture it is much faster.