Extensible Haskell pretty printer. Both a library and an executable. Currently a work in progress (see FIXME items).
$ cabal install hindent
$ hindent
hindent: arguments: --style [fundamental|chris-done|johan-tibell]
Input code:
foo = do print "OK, go"; foo (foo bar) -- Yep.
(if bar then bob else pif) (case mu {- cool -} zot of
Just x -> return (); Nothing -> do putStrLn "yay"; return 1) bill -- Etc
where potato Cakes {} = 2 * x foo * bar / 5This is an intentionally very dumb style that demands extension.
foo =
do print
"OK, go"
foo
(foo
bar)
(if bar
then bob
else pif)
(case mu {- cool -}
zot of
Just x ->
return
()
Nothing ->
do putStrLn
"yay"
return
1)
bill -- Etc
where potato Cakes{} =
2 * x
foo * bar / 5Documented in the style guide. This printer style uses some simple heuristics in deciding when to go to a new line or not, and custom handling of do, if, case alts, rhs, etc.
foo = do
print "OK, go"
foo
(foo bar)
(if bar
then bob
else pif)
(case mu {- cool -} zot of
Just x ->
return ()
Nothing -> do
putStrLn "yay"
return 1)
bill -- Etc
where
potato Cakes{} =
2 * x foo * bar / 5My style is documented in the style guide. This printer style uses some simple heuristics in deciding when to go to a new line or not.
foo =
do print "OK, go"
foo (foo bar)
(if bar
then bob
else pif)
(case mu {- cool -} zot of
Just x -> return ()
Nothing ->
do putStrLn "yay"
return 1)
bill -- Etc
where potato Cakes{} = 2 * x foo * bar / 5In
elisp/hindent.el,
there is the function hindent/reformat-decl which you can run with
M-x hindent/reformat-decl. Or alternatively define a keybinding,
e.g.:
(define-key haskell-mode-map (kbd "C-c i") 'hindent/reformat-decl)By default it uses the style called fundamental, if you want to use
another, john-tibell, run M-x customize-variable hindent-style. If you want to configure per-project, make a file
called .dir-locals.el in the project root directory like this:
((nil . ((hindent-style . "john-tibell"))))No support yet. Patches welcome.
This package comes with a basic fundamental pretty printer, which is probably not desirable to use.
It comes with other styles implemented on top of this fundamental
printer, in the modules in HIndent.Styles.*.
Make a module HIndent.Styles.YourName in which to place the printer.
To define your own, see
HIndent.Styles.Fundamental
for a starting point. This module defines a blank style, adds no
additional extensions. Customizations are specified via the
styleExtenders property. See
HIndent.Styles.ChrisDone
for an example of a non-trivial style.
Useful combinators can be found in
HIndent.Pretty
for defining printers. When you want to use a fundamental printer, use
prettyNoExt instead of pretty. Comments will still be inserted by
prettyNoExt.
If you want to contribute it to the package, add it to the list of styles in HIndent and export it, and open a pull request.
-
Add test suite.
-
Flesh out more obscure parts of the AST.
-
Improve comment re-insertion.
-
Possibly: Support formatting whole modules.
-
Implement some operator-specific layouts: e.g.
Foo <$> foo <*> bar <*> mu