@AdamTornhill FUNCTIONAL PROGRAMMING IN THE REAL WORLD http://www.empear.com/ 

@AdamTornhill My Road To Functional Programming 

Clojure @AdamTornhill My Road To Functional Programming 1980 1990 2000 2010 2015 Assembly C Pascal C++ Java TCL http://www.paulgraham.com/avg.html Erlang J? 

Less Code, More Features, More Fun @AdamTornhill Erlang Java Lines of Code 

The 60/60 Rule @AdamTornhill https://www.amazon.com/Facts-Fallacies-Software-Engineering-Robert/dp/0321117425/ 

What’s Functional Programming? @AdamTornhill “If you ask 100 programmers for their definition, you'll likely receive 100 different answers” — Michael Fogus & Chris Houser Immutability Lambda Calculus Recursion Lazy Evaluation Category Theory Monads Pure Functions Referential Transparency Hindley–Milner type inference 

Immutable State @AdamTornhill i = 41; 

5 ? 1 2 8 3 4 6 7 A Quick Reasoning Test @AdamTornhill 

@AdamTornhill Don’t Turn Your Code Into An IQ Test state Side effects Working memory tax 

IMMUTABILITY ALLOWS PROGRAMS TO SCALE IN COGNITIVE TERMS @AdamTornhill 

TDD: A Diminishing Return in FP @AdamTornhill 

REPL interactions -> soon to become unit tests REPL Driven Development @AdamTornhill 

The Perils Of Test Setup @AdamTornhill Code from https://github.com/aspnet/Mvc 

@AdamTornhill “The length of a test’s setup method is inversely related to the readability of the code under test.” —Adam’s Heuristic 

Unit Tests With Immutable State 0 (ZERO) SETUP METHODS 

Threading Macros @AdamTornhill (defn costs-by-file
 [costs file-name->ticket]
 (->> costs (map (partial assign-to-files file-name->ticket)) (filter passes-thresholds?) (reduce by-file-name))) Readability and Code Evolution 

@AdamTornhill (defn costs-by-file
 [costs file-name->ticket]
 (->> costs (map (partial assign-to-files file-name->ticket)) (filter passes-thresholds?) (reduce by-file-name))) Performance And Lazy Evaluation lazy lazy 

In Introductory Presentations …In The Real World @AdamTornhill Functional Programming 

A Production System in FP @AdamTornhill https://codescene.io/ 

A Production Systems in FP @AdamTornhill https://codescene.io/ CodeScene on-premises Two 

Analysing Android @AdamTornhill Analysis of https://github.com/android/platform_frameworks_base 

@AdamTornhill docs core services packages tools media 

@AdamTornhill 

@AdamTornhill 

@AdamTornhill 

@AdamTornhill 

The Need For Concurrency @AdamTornhill . . . 

Concurrency Made Easy @AdamTornhill Possible (map complexity-trend files) (pmap complexity-trend files) Concurrency Exception! 

Functional Architecture @AdamTornhill MACRO LEVEL: same difference SUB-SYSTEM LEVEL: more freedom ISOLATE SIDE EFFECTS Side effects should be clear and kept to a thin layer at the edge of your system. 

… Social Architectural Pattern: Pipes And Filters Input Sources Git JIRA Teams Transformations Time Users Files Analyses Hotspots Effort Pattern Detectors Risk Neural Nets … Git Time Users Files Hotspots Early Warnings Run-time behaviour Result, purely functional, no side-effects 

Remember The Pipeline Style? @AdamTornhill (defn costs-by-file
 [costs file-name->ticket]
 (->> costs (map (partial assign-to-files file-name->ticket)) (reduce by-file-name) (filter passes-thresholds?))) 

… Social Architectural Pattern: Pipes And Filters Input Sources Git JIRA Teams Transformations Time Users Files Analyses Hotspots Effort Pattern Detectors Risk Neural Nets … Git Time Users Files Hotspots Early Warnings Run-time behaviour Result, purely functional, no side-effects 

Beyond Myths: A Real-World Dirty REST API Domain specific language for describing routes Side-effects: 1. Read from DB 2. Fire-off a pipeline of business logic 3. Write the results to DB, reply 

Finally A Silver Bullet? @AdamTornhill 

LAZY EVALUATION IS GREAT @AdamTornhill …EXCEPT FOR WHEN IT’S NOT 

@AdamTornhill (defn costs-by-file
 [costs file-name->ticket]
 (->> costs (map (partial assign-to-files file-name->ticket)) (reduce by-file-name) (filter passes-thresholds?))) The code we write: clojure.lang.AFn.applyToHelper (AFn.java:152) clojure.lang.AFn.applyTo (AFn.java:144) clojure.core$apply.invokeStatic (core.clj:646) clojure.core$apply.invoke (core.clj:641) codescene.analysis.diagnostics$trace_ns$fn__9583 clojure.lang.RestFn.invoke (RestFn.java:397) clojure.lang.AFn.applyToHelper (AFn.java:152) clojure.lang.RestFn.applyTo (RestFn.java:132) clojure.core$apply.invokeStatic (core.clj:646) clojure.core$apply.invoke (core.clj:641) codescene.analysis.diagnostics$trace_ns$fn__9583 clojure.lang.RestFn.invoke (RestFn.java:397) clojure.lang.AFn.applyToHelper (AFn.java:152) clojure.lang.RestFn.applyTo (RestFn.java:132) clojure.core$apply.invokeStatic (core.clj:646) clojure.core$apply.invoke (core.clj:641) codescene.analysis.diagnostics$trace_ns$fn__9583 clojure.lang.RestFn.invoke (RestFn.java:397) clojure.lang.AFn.applyToHelper (AFn.java:152) clojure.lang.RestFn.applyTo (RestFn.java:132) clojure.core$apply.invokeStatic (core.clj:646) clojure.core$apply.invoke (core.clj:641) codescene.analysis.diagnostics$trace_ns$fn__9583 clojure.lang.RestFn.invoke (RestFn.java:397) clojure.lang.AFn.applyToHelper (AFn.java:152) clojure.lang.RestFn.applyTo (RestFn.java:132) clojure.core$apply.invokeStatic (core.clj:646) clojure.core$apply.invoke (core.clj:641) codescene.analysis.diagnostics$trace_ns$fn__9583 clojure.lang.RestFn.invoke (RestFn.java:397) clojure.lang.AFn.applyToHelper (AFn.java:152) clojure.lang.RestFn.applyTo (RestFn.java:132) clojure.core$apply.invokeStatic (core.clj:646) The exception we get Clojure Specific: The Semantic Gap 

Java — The Assembly Language of the JVM @AdamTornhill Dealing With Performance Issues 

Immutability is Key @AdamTornhill Takeaways Think Pipelines - Functions and Architecture No Silver Bullet - Programming is still hard 

@AdamTornhill Beyond Functional Programming http://www.adamtornhill.com/articles/jlang/beyondfunctional.html The Day I Parsed A Monster http://www.empear.com/blog/parse-a-monster/ Lisp for the Web (free) https://leanpub.com/lispweb Try CodeScene https://codescene.io/ [email protected]