Proposal: Add conspicuously missing Functor instances for tuples

Mario Blažević mblazevic at
Wed Jan 20 14:43:54 UTC 2016

On 16-01-18 04:17 PM, amindfv at wrote:
> I share Henning's concerns. Can someone provide a realistic example
> of where an instance for (,,) or (,,,) *is* desirable?

I'm looking at some examples in production code here at work:

 > firstOfThree (a, b, c) = a
 > onFirstOfThree f = changeNode (\(a, b, c)-> (f a, b, c))

	The triple that's being manipulated is local to a bigger function, and 
the order of its a, b, c parameters is arbitrary. If this code was 
written in presence of the proposed instances, the first parameter would 
likely become the last, and at least the latter function would be dropped:

 > onLastOfThree = fmap

I'm not convinced there's any downside, so I'm +1 on the proposal.

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