Simplify type signatures?

[martijnbastiaan]

E.g.:

traceSignal
  :: forall dom  a
   . ( KnownDomain dom
     , BitPack a
     , NFDataX a
     , Typeable a
     , Waveform a )
  => ..

Can be (AFAIK) reduced to:

traceSignal
  :: forall dom  a
   . ( KnownDomain dom
     , NFDataX a
     , Waveform a )
  => ..

Because

class (Typeable a, BitPack a) => Waveform a where 

I'm also wondering if it's worth adding BitPack to that list or to perhaps create a type alias.

[marijn-qbaylogic]

Hmmmm I vaguely remember the compiler telling me that it's better to keep those constraints because they are directly used, not just through Waveform, but I'm no expert on these things.

What do you mean by "adding BitPack to that list"?

Also, now that I think about it, I think Typeable is only really required for a default implementation and can probably be removed from the class level constraint.

create a type alias

Something like Traceable a where Traceable a ~ BitPack a + Typeable a + ...?

[martijnbastiaan]

What do you mean by "adding BitPack to that list"?

Sorry I meant NFDataX. So:

class (Typeable a, BitPack a, NFDataX a) => Waveform a where

That would mean that Waveform a already implies those superclasses, which would reduce the type signature to:

traceSignal
  :: forall dom  a
   . ( KnownDomain dom
     , Waveform a )
  => ..

It's not that NFDataX is necessary for any methods of the class, but any realistic usage is going to need it, so it might be worth adding.

Something like Traceable a where Traceable a ~ BitPack a + Typeable a + ...?

Yeah, so:

type Traceable a = (BitPack a, Typeable a, ...)

[marijn-qbaylogic]

Hmmm so technically, you could currently create a Waveform instance for a type that is itself not traceable, and use LUTs to do everything in Haskell. I'm not sure whether such a case is realistic - I think it might maybe perhaps be useful for GADTs if you do not want to have to create those extra instances?

[martijnbastiaan]

Yeah I doubt that's realistic. We've done things like this in clash-prelude before, "production" Clash tends to be cluttered with constraints.. Anyway, your call.

[marijn-qbaylogic]

Leaving this for the trace lib rewrite. Might add a Traceable constraint there.