Function to add to Data.List

[Niklas Haas]

On Sun, 06 Apr 2014 00:33:34 +0200, Henning Thielemann <schlepptop at henning-thielemann.de> wrote:
> Not exactly, because sortByKey memorizes the results of 'f' and (sortBy 
> . comparing) recomputes 'f' all the time.

Ah, that occurred to me after reading through the original email again,
sorry for replying prematurely.

Would it be worthwhile to use a strict structure instead of ordinary
2-tuples?