[fulafel]

It's also an interesting case of language extensibility benefits. Spec is just a library. And its spritual predecessor, Prismatic/Plumatic Schema, was also just a library. This enabled the markers of spec to learn from a body of usage when creating spec with an eye of making it a a standard feature, first as the spec.alpha library and hopefully now the final form.

An always-on static type system could not develop this way.