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Working with Snap 1.0


Snap 1.0 isn’t on Hackage yet, but here’s how you can play with it now.

NOTE: This was written using ghc-7.8.3. The repo is on GitHub

First we’ll make a new directory for the project and one for the dependencies, then clone the dependencies for 1.0 that aren’t on Hackage:

<code class="bash" style="overflow-x:auto">mkdir auth_server
cd auth_server
mkdir deps
git clone git@github.com:snapframework/io-streams-haproxy.git deps/io-streams-haproxy
git clone git@github.com:snapframework/snap.git deps/snap
git clone git@github.com:snapframework/snap-core.git deps/snap-core
git clone git@github.com:snapframework/snap-server.git deps/snap-server
git clone git@github.com:snapframework/snap-loader-static.git deps/snap-loader-static
git clone git@github.com:snapframework/heist.git deps/heist
git clone git@github.com:snapframework/snap-templates.git deps/snap-templates

We should have a file structure that looks like this:

  • auth_server/ - deps/ - io-streams-haproxy/
  • snap/
  • snap-core/
  • snap-server/
  • snap-loader-static/
  • heist/

We can now get a scaffolded app using snap-templates.

<code class="bash">cd auth_server/deps/snap-templates
cabal build

Building snap-templates gives us the snap executable that we used to use from the snap project. In the project root, let’s init a new scaffold:

<code class="bash">cd auth_server
./deps/snap-templates/dist/build/snap/snap init

Which leaves us with this structure at the top level:

  • auth_server/ - auth-server.cabal
  • deps/
  • snaplets/
  • src/
  • static/

If you haven’t created a new sandbox for this project, do that now and install the dependencies for the scaffold into the sandbox.

<code class="bash">cd auth_server
cabal sandbox init
cabal install --only-dependencies

We can’t build the app yet, since the scaffold is missing two things. We need to add map-syntax as a dependency to auth-server.cabal and we need to replace noSplices with mempty in Site.hs since noSplices has been deprecated.

First, in auth-server.cabal, under Build-depends add map-syntax:

xmlhtml >= 0.1,
map-syntax >= 0.1

Next, we need to add two imports to src/Site.hs:

<code class="haskell">import Data.Map.Syntax
import Data.Monoid (mempty)

as well as replace noSplices with mempty:


errs = maybe noSplices splice authError


errs = maybe mempty splice authError

We can now build and run the project:

cd auth_server
cabal build

We now have a working Snap 1.0 app to play with. In a future blog post, we’ll explore the creation of a Users service.