The first predicate determines the generator.
> On May 25, 2016, at 8:03 PM, Leon Grapenthin <grapenthinl...@gmail.com> wrote:
>
> Just had a chance to play around with spec. Looks like this is going to
> destroy a lot of problem space :) Thanks.
>
> Probably a bug:
> (s/exercise
> (s/and
> set?
> (s/coll-of
> (s/with-gen keyword?
> #(gen/elements [:s1 :s2 :s3]))
> #{})))
> ;->
> ([#{} #{}] [#{} #{}] [#{} #{}] [#{:o-85:1ywl} #{:o-85:1ywl}] [#{} #{}] [#{}
> #{}] [#{} #{}]
> [#{:_Qi.Qj?dtMZh_s*3.x.sTxm9-E.NHr!?b5f0Ir2.u.+bof*-P.r.m_y**e0ntq.W+*.+?Urxe+Xp+/Q}
>
> #{:_Qi.Qj?dtMZh_s*3.x.sTxm9-E.NHr!?b5f0Ir2.u.+bof*-P.r.m_y**e0ntq.W+*.+?Urxe+Xp+/Q}]
> [#{} #{}] [#{} #{}])
>
> Reverse argument order to s/and and it works.
>
> On Monday, May 23, 2016 at 4:12:29 PM UTC+2, Rich Hickey 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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