I find I spend quite some time editing wiki pages, such as the Haskell.org wiki. However, browser-based
editing leaves a lot to be desired, generally making the editing process
more inefficient and difficult than it needs to be. I suspect that these
inefficiencies hamper contributions, especially in longer texts.
The main problem with wiki editing is the browser-based editor forms
aren't proper editors, so you're just wasting your time using them.
Key missing features are:
- Syntax highlighting
- Regular expressions substitutions
- Spell checking
- Programming tool support (particular for a PL wiki like Haskell.org)
We can fill these holes, and improve efficiency, by using the text-based
browser w3m along
with your favourite text editor, which for me is Vim. w3m is a simple,
fast, terminal browser, which uses an external editor by default, for
editing online forms.
Syntax highlighting for wiki files, with embedded Haskell, and Vim is available
here. Save this to your ~/.vim/syntax directory, and
enable it dynamically when editing online with :setf haskellwiki.
Using your favourite editor from w3m is as simple as setting:
editor: vim -c "setf haskellwiki"
in the w3m configuration screen (type o in w3m to bring
this up). This also enables syntax highlighting by default, including
Haskell fragments embedded in "<haskell>" tags.
And of course, vim being vim, you have access to unix tools via the
shell (such as aspell), programming tools like lambdabot (pointfree refactoring of
wiki code, anyone?) and more.
More
details on text editor support for wiki editing, from a variety of
browsers. Thanks to jgrimes for advice on this.
Finally, for the future, I'd like to investigate a generic mechanism for
exporting wiki pages to a local revision control system, such as darcs. For large wiki subsections I work on, I
currently save files locally in a new darcs repository, edit them, then
upload the subsection in a single pass when complete. This is tedious --
power users should always have a revision control back end to the wiki,
for pushing and pulling changes directly. This is the way this blog is
published: developed in a local darcs repository, and then pushed to a
public repository, which blosxom
then renders. Ideally, preparing wiki articles too should involve only
the editor and a revision control system, for publishing.
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2006-09-11
One of the more oft-requested lambdabot
features finally got implemented today: persistent value bindings. So
lambdabot behaves more like a communal Haskell session.
Let's define a useful combinator:
lambdabot> let eq f g = \x -> f x == g (x::[Int])
Defined.
Which we can refer to as a local binding:
lambdabot> > L.eq head last [1..10]
False
Or pass to QuickCheck:
lambdabot> check head `L.eq` last
Exception: Prelude.head: empty list
Telling us our property isn't quite right. Let's fix that:
lambdabot> let eqnotnull f g = \x -> (not (null x)) ==> f x == g (x::[Int])
Defined.
Which is much more useful:
lambdabot> check head `L.eqnotnull` last
Falsifiable, after 0 tests: [2,0]
Or even something True:
lambdabot> check minimum `L.eqnotnull` (head . sort)
OK, passed 500 tests.
I like having the machine figure stuff like this out for me.
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2006-09-10
planet.haskell.org now supports
syntax highlighting of Haskell code using Malcolm Wallace's
HsColour tool.
To colorise your Haskell fragments, build and install HsColour, and run
it with -css. The following source:
-- main :: IO ()
main = print $ case Just e of
Nothing -> error "no return"
Just x -> x
where e = map (+1) [1..100]
Handed to HsColour, and then prune the head and body tags, leaving a
css-ified pre markup:
$ HsColour -css A.hs | sed '1,/body/d;s,</body>,,;$d'
main = print $ case Just e of
Nothing -> error "no return"
Just x -> x
where e = map (+1) [1..100]
Which uses the css tags defined
Lambdabot's plugin list keeps growing. We now have a
QuickCheck plugin. QuickCheck is a rather spiffy unit test generator/framework,
used particuarly for checking invariants in Haskell libraries.
The lambdabot plugin makes it available from irc or the command line, to
check properties of Haskell code.
Ok, something basic:
lambdabot> check True
OK, passed 100 tests.
A bit more complex:
lambdabot> check False == True
Falsifiable, after 0 tests:
A list property:
lambdabot> check \s -> (reverse . reverse) s == id (s :: [Int])
OK, passed 100 tests.
Or for partial functions:
lambdabot> check \s -> (head . sort) s == minimum (s :: [Int])
Exception: Prelude.head: empty list
Ah, so better specify the precondition:
lambdabot> check \s -> not (null s) ==> (head . sort) s == minimum (s :: [Int])
OK, passed 100 tests.
Or an invalid property:
lambdabot> check \s -> not (null s) ==> (head . sort) s == maximum (s :: [Int])
Falsifiable, after 2 tests:
[1,0]
We can hook this into the free theorem's plugins, just for fun:
lambdabot> free filter
$map f . filter (g . f) = filter g . $map f
lambdabot> check \f g s -> (map (f::Int->Int) . filter (g . f)) s ==
(filter g . map f) (s::T)
OK, passed 100 tests.
And we're already using it to answer language questions! Live from #haskell:
16:46 glguy:: ?type rem
16:46 lambdabot:: forall a. (Integral a) => a -> a -> a
16:46 glguy:: ?type mod
16:46 lambdabot:: forall a. (Integral a) => a -> a -> a
16:46 glguy:: synonyms?
16:51 dons:: ?check \a b -> a `rem` b == a `mod` (b :: Int)
16:51 lambdabot:: Exception: divide by zero
16:51 glguy:: heh
16:51 dons:: ?check \a b -> b > 0 ==> a `rem` b == a `mod` (b :: Int)
16:51 lambdabot:: Falsifiable, after 8 tests:
16:51 lambdabot:: 3
16:51 glguy:: ohhh negative numbers
16:51 dolio:: Ah, there you go. Dividing by negatives is different.
16:51 dons:: ?check \a b -> (a > 0 && b > 0) ==> a `rem` b == a `mod` (b :: Int)
16:52 lambdabot:: OK, passed 100 tests.
16:52 dons:: ?check \a b -> (a < 0 && b > 0) ==> a `rem` b == a `mod` (b :: Int)
16:52 lambdabot:: Falsifiable, after 6 tests:
16:52 lambdabot:: 2
16:52 dons:: QuickCheck++
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2006-09-09
Hot on the tail of Andrew Bromage's free theorems
plugin for Lambdabot, we now have two free theorem generators, thanks to
Janis Voigtlaender and Sascha Boehme's FT tool.
lambdabot> ft map
forall T1,T2 in TYPES. forall h1 :: T1 -> T2, h1 strict.
forall T3,T4 in TYPES. forall h2 :: T3 -> T4, h2 strict.
forall f1 :: T1 -> T3.
forall g1 :: T2 -> T4.
(forall x2 :: T1.
h2 (f1 x2) = g1 (h1 x2))
==> forall x1 :: [T1].
map h2 (t1 f1 x1) = t1 g1 (map h1 x1)
lambdabot> ft foldl1
forall T1,T2 in TYPES. forall h1 :: T1 -> T2, h1 strict.
forall f1 :: T1 -> T1 -> T1.
forall g1 :: T2 -> T2 -> T2.
(forall x2 :: T1.
forall x3 :: T1.
h1 (f1 x2 x3) = g1 (h1 x2) (h1 x3))
==> forall x1 :: [T1].
h1 (t1 f1 x1) = t1 g1 (map h1 x1)
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2006-09-04