Schema-tools & tricks & quick clojure.spec intro: my slides from Clojure Finland 22.6.2016 meetup

1. Clojure Finland 10.3.2016
Tommi Reiman / Metosin
@ikitommi
Schema-tools & tricks

2. Schema-tools & tricks
& quick clojure.spec intro
Clojure Finland 10.3.2016 22.6.2016
Tommi Reiman / Metosin
@ikitommi

3. Schema
• https://github.com/plumatic/schema
• Structural data validation library for Clojure(Script)
– Based on predicates, (almost) just data
• Runtime type-checking
• Documentation for data & functions
• Recursive transformations with coercion and matchers
• Macros for defining schematized functions
• Data generation & completion
• DEMO: basic syntax

4. Schema is real life projects (~all of ours)
• (Optionally) annotate your domain functions and values
with Schema
– Schema def , defschema & defn
– Plumbing defnk , fnk & letk
• Enable schema checking for tests (catching 90% of type
bugs)
• Turn off optional validation in production
• Force coercion when needed / at the system boundaries
• Data coercion between contexts

5. Schemas in web development
• Schema coercions when reading from external sources (JSON, XML,
db, …)
• Schema-based remote apis
– Ring-swagger (https://github.com/metosin/ring-swagger)
– Used by compojure-api,fnhouse-swagger, kekkonen, pedestal-api,yada
• Schemas for the ClojureScript frontend
– Code sharing via cljc (common domain: both data & function to operate on ’em)
– schema-tools for combining ui-views & server-views
• End2end schemas for Clojure(Script)?
– Dynamic Schemas over the wire withTransit (allows only partial validation)
– Resolve the expression problem (new wire-formats, new types)

6. Schema example (with kekkonen.io)

7. Schema-tools (https://github.com/metosin/schema-tools)
• Selectors, transformers, walkers
• Handling of defaults
• Coercion helpers
• DEMO: cut & paste models
• DEMO: declarative transformations
• DEMO: defaults
• DEMO: coercion speed (case RegistryX)

8. Schema-viz (https://github.com/metosin/schema-viz)

9. Schema takeaways
• Schema is awesome for runtime structural validation – for both
system boundaries & tests
• Noise-free syntax with schematized data & function definitions
• Has been de facto in Clojure web (api) development
• Mostly just data, enabling cool things like declarative
transformations

10. clojure.spec
(a quick overview)

11. What is
• a new Integrated system for specification and testing, shipped with Clojure 1.9
• Automatic validation, error reporting, test-data & test generation
• Specs can be written external to the actual functions & data (like core.typed)
• Build from ground-up, recursive,regexps
• (Mutable) Global spec registry
• Form, Conform & Unform, multi-spec
• Function specs on :args,:ret and :fn(!)
• Opinions
– Maps should be open
– Namespaced keywords
– Verification via (generative) tests
• Currently is not
– A runtime validation system
– In alpha6, the :ret and :fn was removed from standard instrumentation,hmph.

12. CODE

13. Function specs
https://clojure.org/guides/spec
+ spec for higher order functions
+ spec for macros
+ multispec for multimethods

14. Spec for runtime validation?
https://clojure.org/guides/spec

15. Coercion?
• Conformers live
within the spec (vs
external with
Schema)
• How can I do custom
conform based on
external info (e.g.
protocol used)

16. Generating data
https://clojure.org/guides/spec

17. Generative testing
https://clojure.org/guides/spec

18. More info about spec
• https://clojure.org/guides/spec
• Slack #clojure-spec (both Rich & Alex seem to hang
out there)
• Changes in the language
– Lot’s of new predicates in clojure.core
– Namespaced maps http://dev.clojure.org/jira/browse/CLJ-1910
– Destructuring http://dev.clojure.org/jira/browse/CLJ-1919

19. Schema, Spec vs Both?

20. Performance
2-6x
faster
Not optimized
for perf, yet.http://muhuk.github.io/validation-benchmark/

21. Differences
• Spec has better support for language level
features like multi-methods and higher order
functions
• Schema supports closed maps & coercion
• Both support data generation & generative
tests
• Schema is not found by Rich Hickey

22. Specs for the web, today?
• Played with a idea to combine the two:
– Convert a pragmatic subset of spec predicates into Schema Predicates
• integer? => s/Int
• boolean? => s/Bool
• (and integer? pos?) => (s/constrained s/Int pos?)
– Use Schema as before (web-libs, snappy coercion etc.)
è https://github.com/metosin/spec-tools & integrate into current apis

23. My 2 cents
• Schema is currently much better for runtime validation (at borders)
– Support (api-docs, api-libs), coercions, performance, low ceremony
• Spec will become de facto way for specifying Clojure systems as it will be
part of the core
– Under active development, let’s enjoy the ride!
– Better runtime validation support via 3rd
party libs
• Low ceremony function & data definitions via extra macros
• Coercions(!)
– Tooling support (IDEs, api-libs)
• At least for now, the can co-exist…
è TODAY: Schema for the boundaries, more spec when things freeze down

24. Thanks!

25. Links
• Schema https://github.com/plumatic/schema
– Schema-tools https://github.com/metosin/schema-tools
– Schema-viz https://github.com/metosin/schema-viz
– Ring-Swagger https://github.com/metosin/ring-swagger
• Spec http://clojure.org/about/spec
– Regular Expressions:
https://en.wikipedia.org/wiki/Regular_expression