woudn't the validation be called a lot more that actually needed? e.g. leaf validates itself, one level up needs to re-validate the leaf as part of it's own validation, etc.

the prismatic approach: https://plumatic.github.io//schema-0-2-0-back-with-clojurescript-data-coercion

Ideally, no, you assume the leaves are already correct if you made it to the parent then you just satisfy the parent condition or combinator

Let's say that each coercer has a success or failure continuation. On failure, we just return, on success, we call the transformation and validation of the next value

Then you need to define the combination semantics for map, sequence, vector, tuple, and, or

Maybe the validation itself can be split to enter/leave

Map could check on enter that it's a map, then coerce its children

This holds as long as a transformer doesnt modify children recursively

Which is true for 99% of cases? So maybe there could be an optimistic coercer which isnt guaranteed to work all the time