user=> (ref [])
#<ref@5fafa486: []>

user=> (ref 1 :validator pos?)
#<Ref@6c484c6b: 1>

=> (ref 0 :validator pos?)
IllegalStateException Invalid reference state  clojure.lang.ARef.validate (ARef.java:33)

=> (dosync (ref-set (ref 1 :validator pos?) 0))
IllegalStateException Invalid reference state  clojure.lang.ARef.validate (ARef.java:33)

=> (dosync (ref-set (ref 1 :validator pos?) 2))
2

user=> (ref [])
#<ref@5fafa486: []>

user=> (ref 1 :validator pos?)
#<Ref@6c484c6b: 1>

(ref [])

`#<ref@5fafa486: []>`


(ref 1 :validator pos?)
</pre
`#<ref@68148555: 1>`

(ref [])
#<ref@5fafa486: []>

(ref 1 :validator pos?)
#<ref@68148555: 1>

(ref [])
; => #\<ref@5fafa486: []>

(ref 1 :validator pos?)
; => #\<ref@68148555: 1>
</ref@68148555:></ref@5fafa486:>

(ref [])
; => #<ref@5fafa486: []="">

(ref 1 :validator pos?)
; => #<ref@68148555: 1>

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(ref 1 :validator pos?)
; => #<ref@68148555: 1=""\>

(ref [])
; => #<ref@5fafa486: []="">

(ref 1 :validator pos?)
; => #<ref@68148555: 1="">

(ref [])
; => #<Ref@5fafa486: []>

(ref 1 :validator pos?)
; => #<Ref@68148555: 1>