RULE traverse = traverse_?

[Henning Thielemann]

On Tue, 31 Mar 2015, Joachim Breitner wrote:

> At a first glance, the rule
>        "traverse == traverse_"
> seems to be sound where the resulting program well-typed, as if it is
> well-typed in both cases, this means that the result was not used.
>
> Of course, an explicit "traverse_" is still useful, but wouldn’t it
> nevertheless be nice to have a sufficient smart compiler?

If it works it will still surprise programmers if the magic does not 
happen for a custom function similar to 'traverse'. E.g. I had a data 
structure with two type parameters and thus two traverse function 
parameters. I think it is better to tell programmers about the general 
problem instead of fixing a selection of instances.