How can I search a hackage package for a function?

Question

Maybe I am missing something, but is there a way to search inside some package on hackage?

Let's say I know that Snap framework has a function called render. How do I find it starting on it's hackage page: http://hackage.haskell.org/package/snap-0.9.0.1

Answer 1

You can use Hoogle for this (as for so many other things) by using the +package search operator.

By default, Hoogle will search inside a standard set of packages by name or by type:

• Searching for traverse will find:
  • traverse :: (Traversable t, Applicative f) => (a -> f b) -> t a -> f (t b)
    base Data.Traversable
  • traverse_ :: (Foldable t, Applicative f) => (a -> f b) -> t a -> f ()
    base Data.Foldable
    Map each element of a structure to an action, evaluate these actions from left to right, and ignore the results.
  • … and so on
• Searching for (a -> b -> c) -> f a -> f b -> f c will find:
  • liftM2 :: Monad m => (a1 -> a2 -> r) -> m a1 -> m a2 -> m r
    base Control.Monad
    Promote a function to a monad, scanning the monadic arguments from left to right.
  • liftA2 :: Applicative f => (a -> b -> c) -> f a -> f b -> f c
    base Control.Applicative
    Lift a binary function to actions.
  • … and so on

Now, that's fine and dandy, but what about other packages? If you search for render, you find Render :: RenderMode from OpenGL, render :: Doc -> String from pretty, and some other things; the snap package isn't searched by default.

However, if you add +packagename or +Module.Name to your search, Hoogle will only search inside the specified packages (and -packagename and -Module.Name remove packages/modules from the search). Thus, searching for +snap render finds only the following three things:

• render :: HasHeist b => ByteString -> Handler b v ()
  snap Snap.Snaplet.Heist
  Renders a template as text/html. If the given template is not found, this returns empty.
• renderAs :: HasHeist b => ByteString -> ByteString -> Handler b v ()
  snap Snap.Snaplet.Heist
  Renders a template as the given content type. If the given template is not found, this returns empty.
• renderWithSplices :: HasHeist b => ByteString -> [(Text, SnapletSplice b v)] -> Handler b v ()
  snap Snap.Snaplet.Heist
  Renders a template with a given set of splices. This is syntax sugar for a common combination of heistLocal, bindSplices, and render.

For more information on using Hoogle, you can check its manual on the Haskell wiki.