Lambda The Extreme: Test-Driving a Functional Language

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λ the eχtremetest-driving a functional language

07/30/2014

PREPARED BYTim [email protected]

mailto:[email protected]

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λ the eχtreme: test-driving a functional language

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“

”


Scala: you stare at your foot for 3 days without any sleep, you then figrue [sic] out how to shoot yourself in the foot with one line of code… recursively.

Comment from Roberto Leibman on How to Shoot Yourself in the Foot in Any Programming Language

by Mike Walker

http://www.fullduplex.org/humor/2006/10/how-to-shoot-yourself-in-the-foot-in-any-programming-language/



4λ the eχtreme: test-driving a functional language

AgendaΛ Tools of the TradeΛ First testΛ A synchronicityΛ Network independenceΛ More of the sameΛ Changing StationΛ And so on and so forth and so on….


Prelude

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The Little Schemer


http://www.amazon.com/The-Little-Schemer-4th-Edition/dp/0262560992

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“

”λ the eχtreme: test-driving a functional language

if you look at the features Scala provides, it is substantially a

functional language, but on the surface it does not always look

like one, and it does not force you to adopt the functional style.

For many of its users, the functional programming constructs in

Scala are the most important set of tools it has to offer but they

are not the only tools. In fact, great care has been spent in the

Scala design to make functional constructs, imperative

constructs, and objects all play well together. I think

postfunctional is a good term for that blend.

- Martin OderskyA Postfunctional Language

http://www.scala-lang.org/old/node/4960





Tools

Λ Git

Λ Maven

Λ Scala IDE

Λ A Dropbox account

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TheBeginning

Where do we start?

We can start atTheBeginning.


How can we dothat?

Check it out!


$ git clone https://github.com/timezra/LambdaTheExtreme.git && cd LambdaTheExtreme $ git checkout tags/TheBeginning

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TheBeginning

We got git, now do we get an elephant?

We get a canary instead.



Canary

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Canary

What does a canaryhave to do with this?

It’s an earlyindication thatsomething has gone very wrong.



$ git checkout tags/Canary


Interlude


Recap

Λ A Case Class

Λ An Object

Λ A FeatureSpec

Λ A FunSpec!

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Canary

Can our canary getaccount info?

Only with aDropbox account.



Actors

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Actors

What happenswhen our accountinfo changes?

Our expectation is wrong.


What happenswhen we changeour expectation?

Our test fails.

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Actors

Why does it fail?

Ourimplementation is wrong.


Where do we findthe rightimplementation?

Look in the upperleft.


$ git checkout tags/Actors

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Actors

How can we callDropbox?

Using HTTP


How will Dropbox know us?

We’ll give it atoken.

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Actors

When will we getour account info?

In the future!



Interlude


Recap

Λ Configuration Management

Λ Implicit conversions

Λ An Actor

Λ An Actor Testkit

Λ The Future!


Care and Feeding

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MinedReading

What happens if wefail?

You tell me!


Do we catch anexception?

We intercept it.

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MinedReading

Sprechen SieDeutsch?

Wenn Sie möchten



$ git checkout tags/MinedReading


Etude


Recap

Λ Stubbing a probe’s return value

Λ Intercepting an expected exception

Λ Iterating over an optional value

<Footer Content: Presentation Title, Partner Name, Other> 32

Putting it out there

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Zed

May I sharesomething withyou?

Of course!


I would rather youput than post.

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Zed

What if I don’t havea file lying around?

You can shareanything you likeover the web.


But how will youknow what itshould look like onthe other side?

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Zed

Who’s Zed?

Maybe Zed canhelp.


Scalaz!


$ git checkout tags/Zed


Interlude

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Zed

Of course!

Does Zed useMonads?


Where’s a gooddefinition of whata Monad is? Anywhere but

urbandictionary.com

http://www.urbandictionary.com/define.php?term=monad

http://www.urbandictionary.com/define.php?term=monad

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Zed

This one is pretty good:You Could Have Invented Monads!


The original is still the best:Monads for functional programming

For today, we can look at them as a wayof chaining operations.

http://blog.sigfpe.com/2006/08/you-could-have-invented-monads-and.html





http://homepages.inf.ed.ac.uk/wadler/papers/marktoberdorf/baastad.pdf


Recap

Λ Implicit transformation from a File to an abstract representation of its contents


Birds of a feather

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Bof

We just need a littlecoordination.

What if I want toshare all mypictures ofcanaries withfriends at once?


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Bof

Recursivetraversal fits a treelike a glove.

How about a littlerecursion?



$ git checkout tags/Bof


Interlude

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CallCC

And on and on?

But what happensif the recursiongoes on and on?


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CallCC

And on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on and on



Recap

Λ Changing recursive traversal to iterative using continuations


To be continued….


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Lambda The Extreme: Test-Driving a Functional Language

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Transcript of Lambda The Extreme: Test-Driving a Functional Language