Hi,
I am writing a function that transforms Specs to another formats (similar
to the JSON Schema). Assuming from this post
<http://www.metosin.fi/blog/clojure-spec-as-a-runtime-transformation-engine/>,
I am not the only one. There is no surprise that I am using
clojure.spec/form. Unfortunately I am not fully satisfied with its
output. To illustrate the problem let's suppose that my transformer will be
used by a third person who like to write its own spec-generating helpers:
(require '[clojure.spec.alpha :as spec])
(spec/def ::forgivable-keyword (spec/conformer (fn [x] (cond (keyword? x) x
(string? x)
(keyword x)
true
::spec/invalid))))
(defn kw-enum [& enum-values] (spec/and ::forgivable-keyword (apply
hash-set enum-values)))
Cool! Let's look how can my transformer cope with it!
(spec/form (kw-enum :a :b :c))
; (clojure.spec.alpha/and :my-ns/forgivable-keyword (clojure.core/apply
clojure.core/hash-set enum-values))
Ouch! Have I just seen a local symbol in the form? I am sorry third person,
I won't be able to transform the output of your spec-generating functions.
Unless they are macros:
(defmacro kw-enum [& enum-values] `(spec/and ::forgivable-keyword ~(apply
hash-set enum-values)))
(spec/form (kw-enum :a :b :c))
; (clojure.spec.alpha/and :my-ns/forgivable-keyword #{:c :b :a})
This approach looks better. How does it work in combination with other
specs?
(spec/form (spec/nilable (kw-enum :a :b :c)))
; (clojure.spec.alpha/nilable (my-ns/kw-enum :a :b :c))
There we are. A third-person's function is in the form. We could use eval to
resolve it, but do we want to? It has been already evaluated once. What if
there are some side effects?
Practically, one has no option to write spec-generating function and
maintain usability of the spec/form at the same time. Therefore one of four
situations must have happened. Either I got something wrong, Specs are not
meant to be introspected, Specs are not meant to be generated or spec/form
is badly designed. Which one is it?
(In the case of the fourth one I have some suggestions, but lets keep them
for later conversation)
Thanks for your time
Marian
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