[hakyll] Good way to have "watch" (or similar) to also rebuild the blog Haskell code and rebuild site when .hs files change?

[Janne Hellsten]

I found a pretty decent way to accomplish what I want (ie., quickly
recompile Haskell when any .hs source file changes + rebuild of the site).

I added this function into my site.hs:

Instead of just the "main :: IO ()" entry point with

main :: IO ()
main = do
E.setLocaleEncoding E.utf8
hakyllWith config buildRules

..I added another entrypoint:

-- For starting with ghcid site.hs --test ghcidEntry
-- forces site recompilation when the .hs source changes.
ghcidEntry :: IO ()
ghcidEntry = do
void $ hakyllWithExitCodeAndArgs config (Options False Clean) buildRules
void $ hakyllWithExitCodeAndArgs config (Options False (Watch
"127.0.0.1" 8000 False)) buildRules

This way I can start my blog with:

ghcid site.hs --test ghcidEntry

Ghcid will reload any changed Haskell code and run the blog. As I added a
"clean" invocation into ghcidEntry, caches are blown so that any outputs
that might depend on my Haskell code will be regen'd.

I'm generating a bunch of SVG outputs (incl. animation) with blaze-svg and
rebuilding the site with "stack build" takes FOREVER, killing any
productivity gains I'd get from developing in Haskell as opposed to say
using Javascript with webpack (the webpack-dev-server supports quick
iteration really well). But ghcid with the added ghcidEntry entry point
makes this a pretty decent experience.

Janne


On Sun, May 20, 2018 at 8:09 PM, Kyle Marek-Spartz <

Making your site.hs executable and deferring type errors to runtime might
https://docs.haskellstack.org/en/stable/GUIDE/#script-interpreter
https://downloads.haskell.org/~ghc/7.10.1/docs/html/users_
guide/defer-type-errors.html

I'd like to embed some SVG diagrams that are generated using Haskell
(either using Diagrams or most probably just dumping svg). I do this by
just adding a module called "Diagrams" which has a bunch of functions that
just output an SVG string. Then I hook these into my blog by adding a
constField into my postCtx. E.g., something like
postCtx :: Context String
postCtx = mconcat
[ modificationTimeField "mtime" "%U"
, dateField "date" "%B %e, %Y"
, snippetField
, constField "diagram1" diagram1Svg
, defaultContext
]
in markdown I can just do $diagram1$ to extract the SVG into my HTML
output.
However, when I edit the Haskell source for diagram1Svg, the blog doesn't
get rebuild when I save the file. This is when using "blog preview".
Is there a way for these to somehow get updated with preview?
I could of course add a watch script myself that calls "stack build &&
stack exec blog build" when any of the .hs files change. But as you all
are probably painfully aware, Haskell builds are slooooow.
I probably could use "ghcid --test" to auto reload the blog and run a
command on each compile. Not sure how I can give command line options for
the "--test" switch in Ghcid though. And it feels like this is something
that'd be better supported by Hakyll out of the box.
Janne
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