A choice at a branch point to take either the left branch or the right branch.

A step in a path through a tree, which can either pass through a point with a cached result or take a choice to go left or right at a branch point.

A sequence of Steps.

Returns the opposite of the given branch choice.

Follows a Path through a Tree to a particular subtree; the main use case of this function is for a processor which has been given a particular subtree as its workload to zoom in on that subtree. The way this function works is as follows: as long as the remaining path is non-empty, it explores the Tree until it encounters either a cache point or a choice point; in the former case the path supplies the cached value in the CacheStep constructor, and in the latter case the path supplies the branch to take in the ChoiceStep constructor; when the remaining path is empty then the resulting Tree is returned.

WARNING: This function is not valid for all inputs; it makes the assumption that the given Path has been derived from the given Tree so that the path will always encountered choice points exactly when the tree does and likewise for cache points. Furthermore, the path must not run out before the tree hits a leaf. If any of these conditions is violated, a WalkError exception will be thrown; in fact, you should hope than exception is thrown because it will let you know that there is a bug your code as the alternative is that you accidently give it a path that is not derived from the given tree but which coincidentally matches it which means that it will silently return a nonsensical result. Having said all that, you should almost never need to worry about this possibility in practice because there will normally be only one tree in use at a time and all paths in use will have come from that tree.

Like sendTreeDownPath, but for impure trees.

This exception is thrown whenever a Tree is sent down a path which is incompatible with it.