Example of a printer that is more suited for instrumentation

gistfile1.txt

user=> (require '[expound.alpha :as expound]
                '[clojure.spec.alpha :as s])
nil
user=> (set! s/*explain-out* (expound/custom-printer {:print-specs? false :show-valid-values? true}))
#object[expound.alpha$custom_printer$fn__895 0x38b972d7 "expound.alpha$custom_printer$fn__895@38b972d7"]
user=> (let [{:keys 4} foo] x)
CompilerException clojure.lang.ExceptionInfo: Call to clojure.core/let did not conform to spec:
-- Spec failed --------------------

  ([{:keys 4} foo] x)
    ^^^^^^^^^

should satisfy

  simple-symbol?

or

  vector?

-- Spec failed --------------------

  ([{:keys 4} foo] x)
           ^

should satisfy

  vector?

-------------------------
Detected 2 errors
 #:clojure.spec.alpha{:problems ({:path [:args :bindings :binding :sym], :pred clojure.core/simple-symbol?, :val {:keys 4}, :via [:clojure.core.specs.alpha/bi
ndings :clojure.core.specs.alpha/bindings :clojure.core.specs.alpha/binding :clojure.core.specs.alpha/binding-form :clojure.core.specs.alpha/binding-form :clo
jure.core.specs.alpha/local-name], :in [0 0]} {:path [:args :bindings :binding :seq], :pred clojure.core/vector?, :val {:keys 4}, :via [:clojure.core.specs.al
pha/bindings :clojure.core.specs.alpha/bindings :clojure.core.specs.alpha/binding :clojure.core.specs.alpha/binding-form :clojure.core.specs.alpha/binding-for
m :clojure.core.specs.alpha/seq-binding-form], :in [0 0]} {:path [:args :bindings :binding :map :keys], :pred clojure.core/vector?, :val 4, :via [:clojure.cor
e.specs.alpha/bindings :clojure.core.specs.alpha/bindings :clojure.core.specs.alpha/binding :clojure.core.specs.alpha/binding-form :clojure.core.specs.alpha/b
inding-form :clojure.core.specs.alpha/map-binding-form :clojure.core.specs.alpha/map-special-binding :clojure.core.specs.alpha/keys], :in [0 0 :keys]}), :spec
 #object[clojure.spec.alpha$regex_spec_impl$reify__2436 0x73aff8f1 "clojure.spec.alpha$regex_spec_impl$reify__2436@73aff8f1"], :value ([{:keys 4} foo] x), :ar
gs ([{:keys 4} foo] x)}, compiling:(NO_SOURCE_PATH:4:1)
user=>