NotesonthehistoryoffunctionalprogrammingandHaskell
                                               June6,2018
                                           SebastianMuskalla
                                              TUBraunschweig
                                             Summerterm2018
             Contents
             Preface                                                                         1
             Literature                                                                      2
             NotesonthehistoryoffunctionalprogrammingandHaskell                              3
             Lecturesyllabus                                                                 9
             Preface
             ThesearenotesforthefirstofmylecturesonfunctionalprogramminginHaskelltaughtatTUBraun-
             schweiginthesummertermof2018. Itcontainsashortoverviewofthehistoryoffunctionalprogram-
             mingandthedevelopmentofHaskell.
             The other lectures that are concerned with presenting Haskell and its concepts are not covered by
             thesenotes(exceptfortheLecturesyllabus)However,thereisanabundanceofmaterialonlearning
             Haskell that anybodywhoisinterestedcanusetogetstarted(seeLiterature). Furthermore,thecode
             examplesthatwereusedinthelectureareavailablehere:
             https://labrador.tcs.cs.tu-bs.de/fp/code_examples.
             In case you spot a bug in these notes, please send me a mail: s.muskalla@tu-bs.de.
             SebastianMuskalla
             Braunschweig,June6,2018
       Literature
       Themainresourcethatwasusedtopreparethelecturesisthebook
       “ThinkingfunctionallywityhHaskell”
       R. Bird.
       CambridgeUniversityPress,2015.
       Otherresourcesthatwereusedinclude:
         • “Software-Entwicklung1”
          A. Poetzsch-Heffter.
          Lectureslides, TUKaiserslautern, 2009(inGerman).
         • “FortgeschrittenefunktionaleProgrammierunginHaskell”
          J. Betzendahl, S. Dresselhaus.
          Lectureslides, Universität Bielefeld, 2016 (in German).
          https://github.com/FFPiHaskell/Vorlesung2016
         • “FunktionaleProgrammierung”
          J. Knoop.
          Lectureslides, TUWien,2017(inGerman).
         • “FortgeschrittenefunktionaleProgrammierung”
          J. Knoop.
          Lectureslides, TUWien,2018.
         • “Methodical, industrial software-engineering using the Haskell functional programming pan-
          guage”
          H.V.Riedel
          Lectureslides, TUWien,2017.
         • “LearnyouaHaskellforgreatgood!”
          MiranLipovača
          NoStarchPress,2011.
          http://learnyouahaskell.com
         • “Functionalprogramming”
          P. Wadler
          Lecture, University of Edinburgh, 2011.
         • “Thefirst monadtutorial”
          P. Wadler
          Talk, YOW!2013.
          https://www.youtube.com/watch?v=yjmKMhJOJos
         • “WhatIWishIKnewWhenLearningHaskell”
          S. Diehl
          http://dev.stephendiehl.com/hask/
         • andtheHaskellWiki,e.g.https://wiki.haskell.org/What_a_Monad_is_not.
               NotesonthehistoryoffunctionalprogrammingandHaskell
               Historyofprogramming
                   • Early computers:  Strict separation between program (e.g. electronic circuits) and data
                     (e.g. punch cards)
                   • von Neumannarchitecture: program and data share the same memory (stored-program com-
                     puters)
                   • von Neumann-style imperative programing:      Commands/statements (representing state
                     changes)vs. expressions(representingdata)
                   • Imperativeprogramsaresequencesofcommands(withjumps,e.g.realizedviago to)
                   • Dijkstra 1968: “Go To statement consideredharmful”
                      ↰
                       Structuredprogramming(if,while,...) &proceduralprogramming
                   • Proceduralprograms: Functionalityrealizedbyproceduresthatcancalleachother
                   • Procedures have explicit parameters and return values, but still have side effects (like reading
                     andwritingtheglobalstateandintersectionwiththeoutsideworld)
                   • John Backus (Fortran language designer) in his Turing Award lecture 1977 “Can programming
                     beliberatedfromthevonNeumannstyle?”
                      ↰
                       Boostofresearchintofunctionalprogramming
               Whatisfunctionalprogramming?
                   • A (pure) function is a procedure without side effects: It can only read immutable parts of the
                     globalstate
                   • Pure functions are functions in the sense of mathematics: If x = y, then f(x) = f(y), no matter
                     wherethisexpressionoccursinthecode.
                   • In functional programming,functionalityisrealizedbycomposingfunctions
                   • In the ideal case: No commands/statements,onlyexpressions
               Historyoffunctionalprogramming
                   • Since1950s: LISPanditsdialects
                   • After Backus’ lecture: Research into functional programming becamepopular...
                   • butitspracticalapplicationswerelimitedtospecialfields(e.g.Erlang(since1986)forcommuni-
                     cationsystems)
                   • In the last 10 years: Rise of functional programming and multi-paradigmlanguages
                        Languages
                              • Non-pure functional languages: LISP (including dialects like Clojure, Scheme), ML (including
                                dialects like (O)Caml), Erlang, …
                              • Multi-paradigmlanguages: Python,Ruby,JavaScript,…
                              • Rise andfall of Scala (around 2010)
                              • SinceJava8(2014)andC++11: SomefunctionalconceptsinJavaandC++
                              • Nowadays: Almost no new language without functional programming (Apples’s Swift, Kotlin,
                                Ceylon). Counter-example: Google’sGo.
                        Haskell
                              • Since1986
                              • NamedafterthelogicianHaskellCurry(1900-1982)
                              • Onlypopularpurefunctionallanguage
                              • AccordingtoR.Bird: Themostradicalfunctionallanguage
                              •      – Compiled(butalsohasaninterpreter)
                                     – Non-strictsemantics,Lazyevaluation
                                     – Strongstatictyping
                                     – Conceptsfromcategorytheorylikemonads
                              • Initially mostly a scientific project, but increasing use in practice in the last years
                        Environment
                              • TheHaskellplatformincludingtheGHCisthede-factostandardimplementation
                              • compilerGHC:(Glorious)GlasgowHaskellCompiler
                              • “interpreter” GHCi: GlasgowHaskellCompilerinteractiveversion
                              • Warning: The default values of some settings (“language pragmas”) differ by default between
                                GHCiundGHC
                              • NopopularIDEspecificallyforHaskell
                              • Usedbymeduringthelecture: IntelliJIDEAwithHaskForceplugin