README.md

Stack-based Clash environment

This is my Clash playground now. If you came from the blog post, you can check out the tag blog for the exact version of code I refered to there.

What's in here

I play with small snippets of Clash code here, but you are probably here for the setup. To use it, just copy code from this repo to your own project.

Stack

This project's Clash HDL project setup uses Stack as the build tool. You can check these files for what I've done:

• stack.yaml
• package.yaml
• .clashi

Theses are set up so that the following use cases work as intended:

• stack repl and stack build: Building Clash code as normal Haskell
  • The configuration sets up the GHC plugins and extensions needed
• stack repl --with-ghc clash: Running the Clash REPL (You can generate HDL from there)

Constraint trick with -XPartialTypeSignatures

Tired of writing all the (HiddenClockResetEnable dom, NFDataX a, Num a, Eq a) constraints? Just enable -XPartialTypeSignatures and -Wno-partial-type-signatures then replace all your constraints with a _.

Before:

foo ::
     ( HiddenClockResetEnable dom
     , Num a, Default a, NFDataX a
     )
    => a -> a -> a
    -> Signal dom a
    -> Signal dom a

After:

foo :: _
    => a -> a -> a
    -> Signal dom a
    -> Signal dom a

Synthesize annotation trick

Have you ever found yourself writing Sythesize annotations like this:

{-# ANN f Synthesize
    { t_name   = "f"
    , t_inputs = [ PortName "a"
                 , PortProduct "" [ PortName "b", PortName "c" ] ]
    , t_output = PortProduct "res" [PortName "q"]
    } #-}

And thought, maybe there's a less verbose way. Well, look no further than -XOverloadedLists and -XOverloadedStrings

instance IsString PortName where
    fromString = PortName

instance IsList PortName where
    type Item PortName = PortName

    fromList = PortProduct ""

    toList = error "toList for PortName is not implemented"

Now we can just write:

{-# ANN f Synthesize
    { t_name   = "f"
    , t_inputs = [ "a", [ "b", "c" ] ]
    , t_output = PortProduct "res" [ "q" ]
    } #-}

Isn't that just like, way more readable?

Note that these are indeed orphans so you might want to put {-# OPTIONS -Wno-orphans #-} in whatever file you are defining these instances.