How would I write a schema for a non-blank string?

Ah, there seems to be a schema/pred

Is there a built in way to generate from regexes?

Managed to find a solution: http://stackoverflow.com/questions/43635022/generate-from-regular-expression-with-plumatic-schema-generators/43635023#43635023

is there a way to create a custom validation function that will act as a predicate?