Realms

Realms are objects that describe the shape of data. First and foremost, they can serve as documentation, describing the data flowing through your programs, similarly to types. (Realms are values though, of course.)

Thus, they are in a similar space as clojure.spec, Schema, and Malli, and we would have loved to avoid creating an alternative. However, we couldn't make any existing system meet all of our requirements:

• support tagged records
• support mixed data aka "sum types"
• function as a description that can be inspected by a program
• enable automatic creation of generators for property-based testing
• fast predicates for data classification
• efficient validation

Ultimately, you'll see that the existing systems focus much of their support on data-as-keyword-keyed maps, which is not a good match for the design-recipes-style development that we favor. (For some background on our motivation, see this video.)