`zen/schema` traversing

[KGOH]

Validation implements zen/schema traversing. There are more applications that need to traverse zen/schema besides validation

They can be split in 3 categories. With data and without.

With data -- use cases alternative to validation. We need to compile schema into a function and apply compiled function to a data:

• Semantic diff (data is some DSL expression, compiled schema is DSL definition)
• Breaking changes analysis
• Generate :text property for some resource

We also may want to transform data:

• Enriching data by setting default values
• Fixing data by type coercing (e.g.: replace arrays with sets if schema says so)

Without data -- we need to compile the whole schema into something else:

• Generating type/object schema for programming languages (e.g.: typescript)
• Generating snapshot schema (super-schema, with symbol definitions inlined in-place of symbols)
• Generating zen/schema viewer & generative documentation
• Generative test data based on a schema

Some may be done in either way:

• Either transforming data or compiling schema into some other DSL (zen FHIR format <-> FHIR format)

If we want to implement any of above, then we need to reimplement all traversing for all zen/schema syntax available and then keep updating this implementation with support of new features that may be introduced into zen/schema that may alter traversing.

I suggest that we need to come up with separate namespace with sole purpose of traversing, which then will be used in zen.v2-validation and in other features we want to implement.

Current zen.walk just uses validation

Severity: high (we need to describe transformations)

[KGOH]

    ;; with update cold
    ;; "Elapsed time: 12.151666 msecs"
    ;; with update warm
    ;; "Elapsed time: 2.454166 msecs"

    ;; without update cold
    ;; "Elapsed time: 18.907042 msecs"
    ;; without update warm
    ;; "Elapsed time: 6.38625 msecs"

    ;; x5000 with update + warm
    ;; "Elapsed time: 2707.391292 msecs"
    ;; x5000 without update + warm
    ;; "Elapsed time: 1868.867417 msecs"