Some material copyright © 1998 by Addison Wesley Longman, Inc. 1Programming Programming LanguagesLanguagesIntroductionSome material copyright © 1998 by Addison Wesley Longman, Inc. 2Overview• Motivation• Why study programming languages?• Some key conceptsSome material copyright © 1998 by Addison Wesley Longman, Inc. 3What is a programming language?“...there is no agreement on what a programminglanguage really is and what its main purpose issupposed to be. Is a programming language atool for instructing machines? A means of communicating between programmers? A vehicle for expressing high-level designs? A notation for algorithms? A way of expressing relationships between concepts? A tool for experimentation? A means of controlling computerized devices? My view is that a general-purpose programming language must be all of those to serve its diverse set of users. The only thing a language cannot be – and survive –is a mere collection of ‘‘neat’’ features.”-- Bjarne Stroustrup, The Design and Evolution of C++ http://www.cs.umbc.edu/331/papers/dne_notes.pdfSome material copyright © 1998 by Addison Wesley Longman, Inc. 4On language and thought (1)“The Language of Thought Hypothesis (LOTH) postulates that thought and thinking take place in a mental language. This language consists of a system of representations that is physically realized in the brain of thinkers and has a combinatorial syntax (and semantics) such that operations on representations are causally sensitive only to the syntactic properties of representations. …”-- Stanford Encyclopedia of Philosophy-- http://plato.stanford.edu/entries/language-thought/Some material copyright © 1998 by Addison Wesley Longman, Inc. 5On language and thought (2)The tools we use have a profound (anddevious!) influence on our thinking habits,and therefore, on our thinking abilities. -- Edsger Dijkstra, How do we tell truths that might hurt?,http://www.cs.umbc.edu/331/papers/ewd498.htmEdsger Wybe Dijkstra (11 May 1930 -- 6 August 2002), http://www.cs.utexas.edu/users/EWD/Professor Edsger Wybe Dijkstra, a noted pioneer of the science and industry of computing, died after a long struggle with cancer on 6 August 2002 at his home in Neunen, the Netherlands.lSome material copyright © 1998 by Addison Wesley Longman, Inc. 6On languages and thought (3)“What doesn't exist are really powerfulgeneral forms of arguing with computers right now. So we have to have special orders coming in on special cases and then think up ways to do it. Some of these are generalizable and eventually you will get an actual engineering discipline.”-- Alan Kay, Educom ReviewAlan Kay is one of the inventors of the Smalltalk programming language and one of the fathers of the idea of OOP. He is the conceiver of the laptop computer and the architect of the modernwindowing GUI.Some material copyright © 1998 by Addison Wesley Longman, Inc. 7Chapter OnePreliminaries, including–Why study PL concepts?–Programming domains–PL evaluation criteria–What influences PL design?–Tradeoffs faced by programming languages–Implementation methods–Programming environmentsSome material copyright © 1998 by Addison Wesley Longman, Inc. 8Why study ProgrammingLanguage Concepts?• Increased capacity to express programming concepts• Improved background for choosing appropriate languages• Increased ability to learn new languages• Understanding the significance of implementation• Increased ability to design new languages• Overall advancement of computingSome material copyright © 1998 by Addison Wesley Longman, Inc. 9Programming Domains• Scientific applications• Business applications• Artificial intelligence • Systems programming• Scripting languages• Special purpose languagesSome material copyright © 1998 by Addison Wesley Longman, Inc. 10Language Evaluation Criteria• Readability• Writability•Reliability• Cost•Etc…Some material copyright © 1998 by Addison Wesley Longman, Inc. 11Evaluation Criteria: ReadabilityHow is it for one to read and understand programs written in the PL?Arguably the most important criterion!Factors effecting readability include:–Overall simplicity»Too many features is bad as is a multiplicity of features–Orthogonality»Makes the language easy to learn and read»Meaning is context independent–Control statements–Data type and structures–Syntax considerationsSome material copyright © 1998 by Addison Wesley Longman, Inc. 12Evaluation Criteria: WritabilityHow easy is it to write programs in the language?Factors effecting writability:–Simplicity and orthogonality–Support for abstraction–Expressivity–Fit for the domain and problemSome material copyright © 1998 by Addison Wesley Longman, Inc. 13Evaluation Criteria: ReliabilityFactors:- Type checking- Exception handling- Aliasing- Readability and writabilitySome material copyright © 1998 by Addison Wesley Longman, Inc. 14Evaluation Criteria: CostCategories:–Programmer training–Software creation–Compilation–Execution–Compiler cost–Poor reliability–MaintenanceSome material copyright © 1998 by Addison Wesley Longman, Inc. 15Evaluation Criteria: othersPortabilityGeneralityWell-definednessEtc…Some material copyright © 1998 by Addison Wesley Longman, Inc. 16Language Design InfluencesComputer architecture- We use imperative languages, at least in part, because we use von Neumann machines- John von Neuman is generally considered to be the inventor of the "stored program" machines - the class to which most of today's computers belong. - CPU+memory which contains both program and data- Focus on moving data and program instructions between registers in CPU to memory locationsSome material copyright © 1998 by Addison Wesley Longman, Inc. 17Von Neumann ArchitectureSome material copyright © 1998 by Addison Wesley Longman, Inc. 18Language Design Influences: Programming methodologies• 50s and early 60s: Simple applications; worry about machine efficiency• Late 60s: People efficiency became important; readability, better control structures. maintainability• Late 70s: Data abstraction• Middle 80s: Object-oriented programming• 90s: distributed programs, internet, web• 00s: Autonomic systems?, pervasive computing? Genetic programming? Semantic web?Some material copyright © 1998 by Addison Wesley Longman, Inc. 19Language CategoriesThe big four:Imperative or procedural (e.g., Fortran, C)Functional (e.g., Lisp,