postcount.hs

-- Get the number of posts that satisfy a pattern
postCount :: Pattern -> Int
postCount pattern = do
  -- something with getMatches sounds right
  m' <- getMatches pattern   -- getMatches :: MonadMetadata m => Pattern -> m [Identifier]
  -- return $ length m' -- Inclined to do return here...
  -- what do I put here?
  
  
-- Other relevant stuff:
-- https://jaspervdj.be/hakyll/reference/Hakyll-Core-Identifier-Pattern.html
postsPattern :: Pattern
postsPattern = "sites/main/_posts/2*.org"

-- From boomerang:
-- How do I use this then?
postCount' :: MonadMetadata m => Pattern -> m Int
postCount' pattern = length <$> getMatches pattern   -- getMatches :: MonadMetadata m => Pattern -> m [Identifier]

Looking at the definition of MonadMetadata it looks like Compiler and Rules are instances of MonadMetadata. So you can call postCount' in a do statement in whatever function with type signature ... -> Rules a or ... -> Compiler a

Boomerang :)