1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
|
---
title: Switch to Hakyll
published: 2015-08-03
tags: Blog Software
---
I stopped using the software suite inherited from
[math.kleen.org](http://math.kleen.org) and switched over to using
[hakyll](http://jaspervdj.be/hakyll/) instead, since I realised that the two
were doing essentially the same job and keeping my mess in one haskell file
(`src/Site.hs`, for those of you who are willing to checkout the
[git repo](https://git.yggdrasil.li/dirty-haskell.org)) instead of spread over a
large number of interlocking zsh and haskell scripts.
I expect nothing to be seriously broken (Only the filepaths of lists have
changed), but some feed readers might have stopped working (hakyll´s
deceptively named `renderRss` actually renders atom).
## Implementation Details
I´m using this post to document some of the more involved things I had to do
during migration in no particular order.
### Lists → Tags
I´m using hakyll´s implementation of
[tags](http://hackage.haskell.org/package/hakyll-4.7.2.2/docs/Hakyll-Web-Tags.html)
instead of the [math.kleen.org](http://math.kleen.org) concept of lists, now.
This required some tweaking.
In order to retain the [All Posts](/tags/all-posts.html) list I introduced a
function to add new tags to an already existing
[Tags](http://hackage.haskell.org/package/hakyll-4.7.2.2/docs/Hakyll-Web-Tags.html#t:Tags)
structure and used it to add my desired pseudo-tag.
~~~ {.haskell}
main = hakyllWith config $ do
…
tags <- buildTags "posts/*" tagTranslation' >>= addTag "All Posts" "posts/*"
…
addTag :: MonadMetadata m => String -> Pattern -> Tags -> m Tags
addTag name pattern tags = do
ids <- getMatches pattern
return $ tags { tagsMap = tagsMap tags ++ [(name, ids)] }
~~~
### Printing lists is an involved affair
I wanted to keep the layout of the site including the lists of posts on the
[index page](/).
Generating those lists turned out to be a hassle.
The `Rule` for `index.md` adds to the context of the templates used in it´s
creation a list field which contains verbatim HTML as produced by renderTag for
each tag.
A trick I used to implement the desired behaviour of replacing old posts with
"…" is to introduce a pseudo post-item which has a flag in it´s context to tell
the corresponding template to only print "…".
Trimming the list of posts is straightforward.
~~~ {.haskell}
renderTag :: String -- ^ Tag name
-> Tags
-> Compiler (Item String)
renderTag tag tags = do
ellipsisItem <- makeItem ""
let
ids = fromMaybe [] $ lookup tag $ tagsMap tags
postCtx = mconcat [ listField "posts" (ellipsisContext ellipsisItem) $
liftM (withEllipsis ellipsisItem) $ chronological =<< mapM load ids
, constField "title" tag
, constField "rss" ("tags/" ++ tagTranslation tag ++ ".rss")
, constField "url" ("tags/" ++ tagTranslation tag ++ ".html")
, defaultContext
]
makeItem ""
>>= loadAndApplyTemplate "templates/post-list.html" postCtx
>>= loadAndApplyTemplate "templates/tag.html" postCtx
where
ellipsisContext item = mconcat [ boolField "ellipsis" (== item)
, defaultContext
]
boolField name f = field name (\i -> if f i
then pure (error $ unwords ["no string value for bool field:",name])
else empty)
withEllipsis ellipsisItem xs
| length xs > max = [ellipsisItem] ++ takeEnd (max - 1) xs
| otherwise = xs
takeEnd i = reverse . take i . reverse
max = 4
~~~
### Everything needs a [Rule](http://hackage.haskell.org/package/hakyll-4.7.2.2/docs/Hakyll-Core-Rules.html#t:Rules)
I was stumped for a while when my templates wouldn´t
[load](http://hackage.haskell.org/package/hakyll-4.7.2.2/docs/Hakyll-Web-Template.html#v:loadAndApplyTemplate).
This was easily rectified by realising, that even templates need (of course) a
declaration of how to compile them:
~~~ {.haskell}
main = hakyllWith config $ do
match "templates/*" $ compile templateCompiler
…
~~~
### Duplicate Rules are duplicate
Hakyll tracks dependencies.
Therefore it seems to keep a list of
[Identifier](http://hackage.haskell.org/package/hakyll-4.7.2.2/docs/Hakyll-Core-Identifier.html#t:Identifier)s
it has encountered with priority given to the more early ones.
It was thus necessary to tweak the function that does `Identifier`/`String`
conversion for tags contained within a
[Tags](http://hackage.haskell.org/package/hakyll-4.7.2.2/docs/Hakyll-Web-Tags.html#v:Tags)
structure if I wanted to use (the very convenient)
[tagsRules](http://hackage.haskell.org/package/hakyll-4.7.2.2/docs/Hakyll-Web-Tags.html#v:tagsRules)
twice.
So I did:
~~~ {.haskell}
main = hakyllWith config $ do
tags <- buildTags "posts/*" tagTranslation' …
let
tags' = tags { tagsMakeId = fromFilePath . (\b -> "rss" </> b <.> "rss") . takeBaseName . toFilePath . tagsMakeId tags}
~~~
|
