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Specs2, go functional

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This document provides an overview of functional programming concepts in Scala including: 1. Referential transparency and immutability which help enable reliable, concurrent programs. 2. Traversal and mapping of data structures in a lazy and composable way using applicative functors. 3. Using reducers for parallel composition and aggregation in a simple way. 4. Representing hierarchical data as trees and providing utilities for traversing trees. 5. Exceptions and configuration as first-class parts of the program flow.

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Specs2, go functional
tour import IncredibleStringReverser._ class ReverserSpec extends Specification { "a reversed empty string must be empty" in { reverse("") must_== "" } "a reversed empty string must really *be empty*" in { reverse("") must be empty } "a reversed string must be reversed abc -> cba" in { reverse("abc") must be_==("cba") } "a longer string must also be reversed. Whoops!" in { reverse("abcdef") must be_==("xxxxx") } }
tour "a reversed empty string must be empty" in { reverse("") must be empty }
tour
tour
Sham e
Mutability
Concurrency
Acceptance
Wh y The idea User Design Program
Go Functional!
Referential transparency Immutability
behavior pipelined F Pemergent behavior Processing data structures OO
Wh y The idea User Design Program
Starting point instructions != expressions
Nesting Precedence: + ! ^
Formatting Text Example Text Example Example
Formatting p br end t, t(i) bt, bt(i) acceptance
Context
doBefore withDb.apply(e2)
Wh y The idea User Design Program
Run execute levels select sequence arguments statistics to text to html
Laziness vs evaluation
Iterating
Traverse A data structure to traverse the accumulation the mapping
Applicative magic? Lots of instances: State List Monad Monoid simple composable Type inference is hard, Lets go shopping!
Reducer aggregation parallel composition mapping specs2 reducers: Levels Statistics Arguments Text Html
Wh y The idea User Design Program
Trees Text Example 1 Example 2 Suite Description Test Description 1 Test Description 2 Suite Description fChildren = TD1, TD2
TreeLoc
TreeLoc Anti-XML The non-violent solution
Concurrency a concurrent task => Promise[Seq[ExecutedFragment]]
Exceptions
Exceptions
Exceptions
Mocks
Mutability Nothing here! Throws exception
Configuration Part of the flow named parameters + defaults nested record
Configuration Implicits implicit arguments default value
Watch out! recursivity val (a,b) = c val in traits lost expressions
Conclusion Reliability Concurrency Composition Less mocks val/vars DSL Type inference Learning curve Gotchas

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Specs2, go functional