Hi, I tried to implement some sort of balancing search tree. For this I need some sort of rotation operation, these need to look a bit deeper (two nodes) into the tree, but I only call them if I already now that these exists (aka are none leafs). But to look into the tree I need to pattern match on …

Probably just do nothing. If you get two nodes, rotate them and return the rotated nodes. If you get anything else just return it as is - the identity function. Maybe need to see some code to give a better recomendation.

First some code (there are 4 rotations (two double rotations and two single rotations) here a single rotation (the double rotations have to look one deeper and have one patternmatch more): single_L : a -> Tree a -> Tree a -> Tree a single_L el lst rst = case rst of E -> undefined T el2 _…

I would be interested in seeing the code that calls single_L as well. Since it’s already doing the pattern matching, can it pass in el, rlst, and rrst instead of rst?

“No runtime errors” is a very high priority for Elm. This means that you are not allowed to create functions that can fail. (Unless you’re implementing a core function like modBy 0.) The unsatisfying the solution of choosing a default value is probably your best choice. What I would do is: Use Deb…

What to do if you have a Non Exhaustive pattern match

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What to do if you have a Non Exhaustive pattern match

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