Hasmin - A Haskell CSS Minifier

Aside from the usual techniques (e.g. whitespace removal, color minification,
etc.), the idea was to explore new possibilities, by implementing things
other minifiers weren’t doing, or they were, but not taking full advantage of.
Also, the minifier implements some techniques that do nothing for minified
sizes, but attempt to improve post-compression sizes (at least when using
DEFLATE, i.e. gzip).
For a list of techniques, see the wiki.
To use it as a library, see
below.
Building & Installing
Stack
The easiest and prefered way is using
stack. Clone the repo, then:
$ cd path/to/hasmin/repo
$ stack build
After that, you can install it with stack install
(installs by default to ~/.local/bin
).
If you’d rather just try it out, use stack exec hasmin
(keep in mind it has
a slight additional delay at the beginning when run this way).
Cabal
Alternatively, you can use cabal:
$ cd path/to/hasmin/repo
$ cabal update # Make sure to have the latest package list
$ cabal sandbox init # Initialise a sandbox
$ cabal install --only-dependencies # Install dependencies into the sandbox
$ cabal build # Build hasmin inside the sandbox
Minifier Usage
Hasmin expects a path to the CSS file, and outputs the minified result to
stdout. Say you have a sheet.css
and want to minify it, and save it as
sheet.min.css
. Then, run:
$ hasmin sheet.css > sheet.min.css
Every technique is enabled by default, except for:
- Escaped character conversions (e.g. converting
\2714
into ✔
, enabled
with --convert-escaped-characters
).
- Dimension minifications (e.g. converting
12px
to 9pt
, enabled with
--dimension-min
, or just -d
).
- Lexicographical sorting of declarations (enabled with
--sort-declarations
).
The first two are disabled mainly because they are—on average, not
always—detrimental for DEFLATE compression. As for declaration sorting, whether
it benefits or hurts compression rates is very stylesheet-dependent, and the
current implementation is quite naive, hence unsafe.
When something needs to be disabled, use the appropriate flag. Not every
technique can be toggled, but if there is any one in particular that you need to
and can’t, open an issue about it.
Note: there is a problem in Windows when using the
--convert-escaped-characters
flag to enable the conversion of escaped
characters. A workaround is changing the code page, which can be done by running
chcp 65001
in the terminal (whether cmd, or cygwin).
Library
The preferable way to use Hasmin as a library is to import Hasmin
; a usage
example can be seen in the module’s documentation.
That is currently the only module that is sure to abide by
PVP. Most other exposed modules are so because tests
need it, and thus definitions there may be changed anytime. In case something
internal is needed though, feel free to open an issue about it.
Zopfli Integration
Hasmin uses bindings to Google’s
Zopfli library, allowing the
possibility to compress the result.
Since the output is a gzip file, it can be used for the web. It tipically
produces files 3~8% smaller than zlib, at the cost of being around 80 times
slower, so it is only a good idea if you don’t need compression on the fly.
Zopfli is released under the Apache License, Version 2.0.