truss VS plumbing

When type checking is needed, I find the Truss library* does the trick quite well.

As for the syntax, there is very little, which can make it a harder lift but once you have the hang of it you won't deal with the issues identified in the parent comment.

* https://github.com/taoensso/truss

I use truss extensively throughout my code to prevent those types of errors.

I haven't tried it myself. I generally just use truss for runtime constraint checking. I use a modified version that integrates scope-capture. And malli validation for more complex cases, but I try to limit that. For me it is better to validate individual attributes as needed, vs validating an entire "type"/collection of attributes. So each function only cares about the attributes that it needs, and validates only as needed.

Use assertions for all data requirements inside functions - I use a modified version of https://github.com/ptaoussanis/truss to ensure that I never get NullReference exceptions, and this also helps make functions more self-documenting. Also use this to assert return data.

This library https://github.com/plumatic/plumbing, a predecessor of spec, has variants of defn and fn that allow you to specify the schema inline, sort of similar to type hints.

This reminds me a bit of a Clojure library called Plumbing (formerly Graph): https://github.com/plumatic/plumbing. It also let you create a DAG for structured computation. It was used for a web service, at that time.