Isn't s redefined in this example:

user=> (require '[clojure.spec :as s])
(s/def ::even? (s/and integer? even?))
(s/def ::odd? (s/and integer? odd?))
(s/def ::a integer?)
(s/def ::b integer?)
(s/def ::c integer?)
(def s (s/cat :forty-two #{42}
              :odds (s/+ ::odd?)
              :m (s/keys :req-un [::a ::b ::c])
              :oes (s/* (s/cat :o ::odd? :e ::even?))
              :ex (s/alt :odd ::odd? :even ::even?)))
user=> (s/conform s [42 11 13 15 {:a 1 :b 2 :c 3} 1 2 3 42 43 44 11])
{:forty-two 42,
 :odds [11 13 15],
 :m {:a 1, :b 2, :c 3},
 :oes [{:o 1, :e 2} {:o 3, :e 42} {:o 43, :e 44}],
 :ex {:odd 11}}


in http://clojure.org/about/spec


On Mon, May 23, 2016 at 5:12 PM, Rich Hickey <richhic...@gmail.com> wrote:

> Introducing clojure.spec
>
> I'm happy to introduce today clojure.spec, a new core library and support
> for data and function specifications in Clojure.
>
> Better communication
>
> Clojure is a dynamic language, and thus far we have relied on
> documentation or external libraries to explain the use and behavior of
> functions and libraries. But documentation is difficult to produce, is
> frequently not maintained, cannot be automatically checked and varies
> greatly in quality. Specs are expressive and precise. Including spec in
> Clojure creates a lingua franca with which we can state how our programs
> work and how to use them.
>
> More leverage and power
>
> A key advantage of specifications over documentation is the leverage they
> provide. In particular, specs can be utilized by programs in ways that docs
> cannot. Defining specs takes effort, and spec aims to maximize the return
> you get from making that effort. spec gives you tools for leveraging specs
> in documentation, validation, error reporting, destructuring,
> instrumentation, test-data generation and generative testing.
>
> Improved developer experience
>
> Error messages from macros are a perennial challenge for new (and
> experienced) users of Clojure. specs can be used to conform data in macros
> instead of using a custom parser. And Clojure's macro expansion will
> automatically use specs, when present, to explain errors to users. This
> should result in a greatly improved experience for users when errors occur.
>
> More robust software
>
> Clojure has always been about simplifying the development of robust
> software. In all languages, dynamic or not, tests are essential to quality
> - too many critical properties are not captured by common type systems.
> spec has been designed from the ground up to directly support generative
> testing via test.check https://github.com/clojure/test.check. When you
> use spec you get generative tests for free.
>
> Taken together, I think the features of spec demonstrate the ongoing
> advantages of a powerful dynamic language like Clojure for building robust
> software - superior expressivity, instrumentation-enhanced REPL-driven
> development, sophisticated testing and more flexible systems. I encourage
> you to read the spec rationale and overview  http://clojure.org/about/spec.
> Look for spec's inclusion in the next alpha release of Clojure, within a
> day or so.
>
> Note that spec is still alpha, and some details are likely to change.
> Feedback welcome.
>
> I hope you find spec useful and powerful!
>
> Rich
>
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-- 
Kind Regards,
Atamert Ölçgen

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www.muhuk.com

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