This is a self-contained Liquid Haskell example.
nix-shell --run "make run"Consider the function apiCallProvideRedundancy.
Imagine it's a part of "Core API" that needs to be safe and free from redundant case-analysis of input data.
Liquid Haskell helps us to express types and filter values based on predicates that go beyond NonEmpty kinds of constructors.
As soon as I declare that type Destinations is a list of at least two non-empty textual values,
the compiler requires me to prove that the data I call apiCallProvideRedundancy with does satisfy
that criteria of the firsrt argument.
Hence the helper parsing functions
have to exist at the boundaries of my API, and not somewhere inside apiCallProvideRedundancy.