Add Counter a => Counter (Vec n a) instance #2787

[gergoerdi]

Fixes: #2787

[leonschoorl]

I think it would be good if the instance came with a comment about the endianness.
Something like

clash-compiler/clash-prelude/src/Clash/Class/Counter/Internal.hs

Lines 156 to 168 in 96f741d

	-- | Counters on tuples increment from right-to-left. This makes sense from the
	-- perspective of LSB/MSB; MSB is on the left-hand-side and LSB is on the
	-- right-hand-side in other Clash types.
	--
	-- >>> type T = (Unsigned 2, Index 2, Index 2)
	-- >>> countSucc @T (0, 0, 0)
	-- (0,0,1)
	-- >>> countSucc @T (0, 0, 1)
	-- (0,1,0)
	-- >>> countSucc @T (0, 1, 0)
	-- (0,1,1)
	-- >>> countSucc @T (0, 1, 1)
	-- (1,0,0)

I like examples like that, because I can never remember which way round is supposed to be big or little.

[leonschoorl]

Also this endianness you implemented now is the "right" one I think.
Because it is consistent with the view encoded in BitPack/Clash.Class.BitPack.BitIndex:

clashi> countSucc @(Vec 3 Bit) (0 :> 0 :> 0 :> Nil)
0 :> 0 :> 1 :> Nil
clashi> msb @(Vec 3 Bit) (0 :> 0 :> 1 :> Nil)
0
clashi> lsb @(Vec 3 Bit) (0 :> 0 :> 1 :> Nil)
1

[martijnbastiaan]

@kloonbot run_ci ca3cba0

[martijnbastiaan]

Agreed with @leonschoorl on the examples / doctests. Other than that, LGTM.

[gergoerdi]

Where are we on this?

[martijnbastiaan]

@kloonbot run_ci ec242f6

[martijnbastiaan]

I'm okay with this if CI is.