21 KiB
Haskell layer
- Description
- Install
- Key bindings
- Syntax checking
- FAQ
- The REPL doesn't work
- The REPL is stuck
- Indentation doesn't reset when pressing return after an empty line
- Flycheck displays HLint warnings but not errors
- HLint fails with parse error
- I can see highlighted errors but they don't appear in the error list
- Flycheck doesn't work
- Flycheck doesn't work with
stack
- haskell-mode commands don't work
Description
This layer adds support for the Haskell language.
Features:
- syntax highlighting for haskell source, cabal files, C– source,
- auto-completion with one of the selected backends (
dante
orlsp
).
This layer is under construction, it needs your contributions and bug reports.
Install
Layer
To use this configuration layer, add it to your ~/.spacemacs
. You will need to
add haskell
to the existing dotspacemacs-configuration-layers
list in this
file.
Dependencies
This layer requires some cabal packages:
apply-refact
(required byhlint-refactor
)hlint
(required byhlint-refactor
)stylish-haskell
(optional forhaskell-mode
)hasktags
(optional)hoogle
(optional forhaskell-mode
andhelm-hoogle
)
To install them, use the following command (or the stack
equivalent):
$ cabal install apply-refact hlint stylish-haskell hasktags hoogle
Setup PATH
First of all, make sure that your $PATH
contains the installation path for
Haskell tools like ghc
, ghci
etc. It depends on how you have installed
ghc
, but you can always check it by running which ghc
in your terminal.
Stack
users should only add the installation path of stack
itself. Usually
it's ~/.local/bin
.
Then make sure that your $PATH
contains the installation path for the cabal
packages. If you are using cabal
it should be ~/.cabal/bin
or
~/Library/Haskell/bin
(for 'Haskell for Mac' users). If you are using stack
then it should be ~/.local/bin
.
For information about setting up $PATH
, check out the corresponding section in
the FAQ (SPC h SPC $PATH RET
).
Choosing a backend
First, ensure that you have auto-completion
layer enabled.
To choose a haskell backend, set the haskell layer variable haskell-completion-backend
:
(haskell :variables haskell-completion-backend 'dante)
Supported values for haskell-completion-backend
are dante
and lsp
.
If you haven't specified any value for haskell-completion-backend
,
dante
will be used as default backend, unless the layer lsp
is enabled,
in which case lsp
is used as default backend.
Backend can be chosen on a per project basis using directory local variables
(files named .dir-locals.el
at the root of a project). An example of .dir-locals.el
to use the
lsp
backend:
;;; Directory Local Variables
;;; For more information see (info "(emacs) Directory Variables")
((haskell-mode (haskell-completion-backend . lsp)))
Note: you can easily add a directory local variable with SPC f v d
.
dante
[[https://github.com/jyp/dante][Dante]] is a fork of Intero mode which aims exclusively at providing a convenient frontend to GHCi.
It brings features like syntax checking, auto completion, hlint suggestions, automatic error fixing, info at point, definition and use sites.
dante
works for cabal
, nix
, sytx
, and stack
users and requires no additional setup.
dante
requires Emacs 25.
lsp
lsp
requires an appropriate installation of hie
, the official Haskell language server, to work properly.
hie
is best installed by building it locally as it requires that the same GHC version has been used to
compile your code as has been used for hie
.
To install it please refer to the official installation instructions here.
Enabling the lsp
backend requires the lsp
layer to be enabled, and provides access to
all the additional lsp-mode
key bindings. As such it is more of a full backend than just
a completion backend.
Alternatively, you can use Haskell Language Server instead of hie
(check their docs for installation details).
Haskell Language Server is meant to completely replace hie
but it is still in early stages of development.
Optional extras
The Haskell layer supports some extra features, which can be enabled through the layer variables.
structured-haskell-mode
Currently there is no support for structured-haskell-mode, since it doesn't play
very well with non-emacs editing styles (structured-haskell-mode/#81). Emacs
editing style users can easily enable it by adding structured-haskell-mode
to
the list of dotspacemacs-additional-packages
in your .spacemacs
file. For
more installation instructions, please refer to the official documentation at
the structured-haskell-mode page. In case you are a non-emacs editing style user
and still want to use structured-haskell-mode
- use it at your own risk.
Any contributions that will help to solve issues with structured-haskell-mode
are warmly welcome!
hindent
hindent is an extensible Haskell pretty printer, which lets you reformat your
code. You need to install the executable with cabal install hindent
or
stack install hindent
.
To enable it you have to toggle the variable haskell-enable-hindent
.
See examples here.
(setq-default dotspacemacs-configuration-layers
'((haskell :variables haskell-enable-hindent t)))
Key bindings
All Haskell specific bindings are prefixed with the major-mode leader SPC m
.
Top-level commands are prefixed by SPC m
:
Key binding | Description |
---|---|
SPC m g g |
go to definition or tag |
SPC m g i |
cycle the Haskell import lines or return to point (with prefix arg) |
SPC m F |
format buffer using haskell-stylish |
SPC m f |
format declaration using hindent (if enabled) |
Documentation
Documentation commands are prefixed by SPC m h
Key binding | Description |
---|---|
SPC m h d |
find or generate Haddock documentation for the identifier under the cursor |
SPC m h f |
do a helm-hoogle lookup |
SPC m h h |
do a Hoogle lookup |
SPC m h H |
do a local Hoogle lookup |
SPC m h i |
gets information for the identifier under the cursor |
SPC m h t |
gets the type of the identifier under the cursor |
Debug
Debug commands are prefixed by SPC m d
:
Key binding | Description |
---|---|
SPC m d a |
abandon current process |
SPC m d b |
insert breakpoint at function |
SPC m d B |
delete breakpoint |
SPC m d c |
continue current process |
SPC m d d |
start debug process, needs to be run first |
SPC m d n |
next breakpoint |
SPC m d N |
previous breakpoint |
SPC m d p |
previous breakpoint |
SPC m d r |
refresh process buffer |
SPC m d s |
step into the next function |
SPC m d t |
trace the expression |
Debug Buffer
Key binding | Description |
---|---|
RET |
select object at the point |
a |
abandon current computation |
b |
break on function |
c |
continue the current computation |
d |
delete object at the point |
i |
step into the next function |
r |
refresh the debugger buffer |
s |
go to next step to inspect bindings |
S |
go to previous step to inspect the bindings |
t |
trace the expression |
REPL
REPL commands are prefixed by SPC m s
:
Key binding | Description |
---|---|
SPC m s b |
load or reload the current buffer into the REPL |
SPC m s c |
clear the REPL |
SPC m s s |
show and switch to the REPL |
SPC m s S |
show the REPL without switching to it |
C-j |
switch to next history item |
C-k |
switch to previous history item |
C-l |
clear the REPL |
Cabal commands
Cabal commands are prefixed by SPC m c
:
Key binding | Description |
---|---|
SPC m c a |
cabal actions |
SPC m c b |
build the current cabal project, i.e. invoke cabal build |
SPC m c c |
compile the current project, i.e. invoke ghc |
SPC m c v |
visit the cabal file |
Cabal files
These commands are available in a cabal file.
Key binding | Description |
---|---|
SPC m d |
add a dependency to the project |
SPC m b |
go to benchmark section |
SPC m e |
go to executable section |
SPC m t |
go to test-suite section |
SPC m m |
go to exposed modules |
SPC m l |
go to library section |
SPC m n |
go to next subsection |
SPC m p |
go to previous subsection |
SPC m s c |
clear the REPL |
SPC m s s |
show the REPL without switching to it |
SPC m s S |
show and switch to the REPL |
SPC m N |
go to next section |
SPC m P |
go to previous section |
SPC m f |
find or create source-file under the cursor |
Refactor
Refactor commands are prefixed by SPC m r
:
Key binding | Description |
---|---|
SPC m r b |
apply all HLint suggestions in the current buffer |
SPC m r i |
reformat imports from anywhere in the buffer |
SPC m r r |
apply the HLint suggestion under the cursor |
Only some of the HLint suggestions can be applied.
Syntax checking
At the moment there are three components, which can indicate errors and warnings in the code. Those components are:
- dante (via flycheck)
- hlint (via flycheck)
- haskell-mode interactive
Since all of these components can be active at the same time, it can be tricky to
know which component is displaying which message, especially when they disagree,
or if one isn't working. Only flycheck errors (from ghci and hlint) are displayed in
the error list and can be navigated between, using the standard Spacemacs key
bindings (under SPC e
) even though errors from other modes might highlight the
actual buffer.
Flycheck
This is the standard Spacemacs way of syntax checking, and it's also the most elaborate. You need to install the syntax-checking layer first, which will bring flycheck. Please read the layer's documentation on how to interact with flycheck.
Flycheck has different Haskell checkers: haskell-dante
, haskell-ghc
, haskell-stack-ghc
and
haskell-hlint
. Normally it can detect the best one to use automatically, but
if it doesn't work, then you can change it with SPC e s
.
HLint
HLint is a linter for Haskell. It doesn't detect errors (as long as it can parse the file) but bad coding style and code smell. The HLint checker is called after the flycheck GHC checker.
HLint can be configured via .hlint.yaml.
Interactive haskell-mode
Finally, interactive haskell-mode (SPC m s b
) also displays errors. These
errors can be navigated to, from the interactive buffer (by clicking on the
error) or using haskell-goto-next-error
(M-n
) and haskell-goto-prev-error
(M-p
).
Flymake
An alternative to syntax checking is to build your projects with
flymake-compile
. It doesn't highlight errors in the buffer, but it's more
reliable. The error navigation is similar to interactive haskell-mode.
Troubleshooting
Flycheck can fail silently for miscellaneous reasons. See the FAQ for troubleshooting.
FAQ
The REPL doesn't work
Usually haskell-mode
is great at figuring out which interactive process to
bring up. But if you are experiencing problems with it, then you can help
haskell-mode
by setting haskell-process-type
as in following code:
(setq-default dotspacemacs-configuration-layers
'((haskell :variables haskell-process-type 'stack-ghci)))
Available options are:
- ghci
- cabal-repl
- cabal-new-repl
- cabal-dev
- cabal-ghci
- stack-ghci
The REPL is stuck
Make sure that there's a space between the REPL's λ>
prompt and the cursor.
When there is no space, then the REPL will behave as if it's stuck. Usually,
when you enter normal state, the cursor moves backwards by one character, so there
is no required space when you switch to insert mode. There is a possible
workaround - just add the following snippet to your dotspacemacs/user-config
function:
(when (configuration-layer/layer-used-p 'haskell)
(add-hook 'haskell-interactive-mode-hook
(lambda ()
(setq-local evil-move-cursor-back nil))))
It makes the cursor stay in the right place in the REPL buffer when you enter normal state. Which in most cases helps you to avoid the problem with 'stuck' REPL.
Also, some users might want to start the REPL in insert mode. This is done by
placing the following snippet in your dotspacemacs/user-config
function:
(when (configuration-layer/layer-used-p 'haskell)
(defadvice haskell-interactive-switch (after spacemacs/haskell-interactive-switch-advice activate)
(when (eq dotspacemacs-editing-style 'vim)
(call-interactively 'evil-insert))))
Indentation doesn't reset when pressing return after an empty line
This is the intended behavior in haskell-indentation-mode
. If you want to
reset the indentation when pressing return after an empty line, add the
following snippet into your dotspacemacs/user-config
function.
(defun haskell-indentation-advice ()
(when (and (< 1 (line-number-at-pos))
(save-excursion
(forward-line -1)
(string= "" (s-trim (buffer-substring (line-beginning-position) (line-end-position))))))
(delete-region (line-beginning-position) (point))))
(advice-add 'haskell-indentation-newline-and-indent
:after 'haskell-indentation-advice)
Flycheck displays HLint warnings but not errors
The HLint checker is called after the normal flycheck checker, even if the checker fails. Check the Flycheck doesn't work section.
HLint fails with parse error
If HLint is not correctly configured (e.g. does not load some extensions that you are using in your project) it might fail while parsing the file.
Check HLint docs for more details.
I can see highlighted errors but they don't appear in the error list
The error list is only set by flycheck. You are probably seeing errors highlighted by haskell-mode. Check the Flycheck doesn't work section.
Flycheck doesn't work
You can use the flycheck-compile
command to check what's wrong with flycheck.
This will show you the exact command line that's used, and its output.
If you are using stack
, check the Flycheck doesn't work with stack
section.
Flycheck doesn't work with stack
First check that flycheck uses the correct checker, and all the paths are
properly configured using flycheck-verify-setup
(SPC e v
). You can force the
checker with flycheck-select-checker
(SPC e s
) to ensure that it uses
haskell-stack-ghc
. If it still doesn't work, then it could be one of the
following problems:
- The
stack
build directory is wrong - The project root is not set properly
The stack
build directory is wrong
The path to the build directory, which contains some generated files, is
normally under .stack-work/install/<os>/Cabal-<version>/build
.
However the version of the cabal library that's used by stack
to generate the
directory name is not the version of the cabal library that's installed by
stack
but rather the version of cabal that's associated to the GHC version.
This error can happen after upgrading cabal or cabal-install. To check if this
is the problem, compare the path name of the build path that's used by flycheck
using flycheck-compile
and compare it to the actual path in the .stack-work
directory. If they are different, then you'll need to reinstall ghc using the
command stack setup --upgrade-cabal
.
The Project root directory is not set properly
Flycheck launches the GHC command, not from the project root directory, but from the directory of the file that's being checked. This is normally not a problem, as all the paths are set properly, however it could be a problem if some template Haskell functions use relative paths (e.g. in Yesod scaffolded projects).
Until it's fixed in flycheck, the workaround is to wrap the stack
command in
order to run all subcommands from the project's root directory. You can do so
with the following script:
#!/bin/bash
cd `stack path --project-root`
stack $*
Make sure you set flycheck-haskell-stack-ghc-executable
to this script.
haskell-mode commands don't work
Some (most) of the haskell-mode commands only work when haskell-mode is in
interactive mode, i.e. has an interactive session associated with it. Load it
using SPC m s b
.