By search, I mean a backtracking search over a 'graph' of possibilities.

There is a well-known pretty printing library by Joh Hughes. It is for 
Haskell but can be made to work on ML style languages by introducing some 
laziness explicitly. Haskell is lazy by default, which is why it is not 
needed there.

http://belle.sourceforge.net/doc/hughes95design.pdf

It defines lambdas that evaluate to the various possible choices then only 
evaluates the 'best' choice according to a heuristic for evaluating pretty 
printing possibilities. I think when a bad choice deeper down is uncovered, 
it can backtrack? To be honest, I never really analysed the code and fully 
understood it, just made use of it or blindly ported it to ML.

Is there some library for Elm that helps with coding this kind of search? 
Or a simpler example illustrating the technique?

I am trying to do a 2d layout algorithm, and thinking of some heuristic 
that will choose amongst various layouts, trying simpler and more symmetric 
options first.

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