Lecture 1. Programming II. Iztok Savnik, FAMNIT. October, 2015.

Transcription

1 Lecture 1 Programming II Iztok Savnik, FAMNIT October,

2 Contents Course outline History of programmiing languages Concepts of programming languages Meta-Language ML Some benchmarks Method and aims of course

3 Course organization Lectures Iztok Savnik Exercises Matjaž Krnc Homeworks Writting programs in Ocaml 4 homeworks

4 Grading Written exam 40% Oral exam 20% Homeworks 40% Each part must be positive! 4

5 Literature 1. John Mitchell, Concepts in Programming Languages, Cambridge Univ Press, Iztok Savnik, Koncepti programskih jezikov, Skripta (in Slovene), FAMNIT, Michael L. Scott, Programming Language Pragmatics (3rd ed.) Elsevier,

6 Overview of PL Assembler Fortran Cobol Imperative languages Algol Prog.language C Pascal, Modula Functional languages Lisp ML Haskell Object languages C++, Objective C Java, Eifel Ruby High-level languages Electronics Information systems Integration languages Script languages System languages Web languages User interfacesi Python, PhP, JSP, ASP Prolog Sicstus Prolog SWI-Prolog Datalog Lambda Prolog

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8 Assembler ALU Registers Instructions and operands Different types of addressing Macros Processors

9 Fortran John W. Backus, 1953, IBM Mathematical FORmula TRANslating System IBM 360 Constructs of Fortran DO, GOTO, IF, SUBRUTINE, CALL Numeric processing Programs can be parallelized Fortran II, Fortran 77, Fortran III, Fortran 90, Fortran 95, Fortran 2003,...

10 Cobol Prog.language for bussiness applications Grace Murray Hopper, >1950 PL based on natural language Awkward syntax Cobol pograms work today! Syntax has been changed

11 Algol Family Functions (procedure) Function has parameters Function returns result We will study functions in detail! Block-oriented language begin end Algol, Pascal, C, Delphi, Modula

12 C Programming Language Dennis Ritchie, Bell Laboratories, 1972 C designed for Language B, based on BCPL Language constructs Algol family Still one of best languages (C++ =? C + object illusion) Close to hardware, system programming Arrays and references are closely related E1[E2] = ]*((E1)+(E2)) Adress arithmetic Ritchie wrote: C is quirky, flawed, and a tremendous success.

13 Pascal Niklaus Wirth, ETH Zürich, 1970 Very popular in Europa Structred programming language Algol family Data structures, pointers, arrays, variable records,... Many implementations VAX Pascal, Turbo Pascal, Delphi: nice programming environment Modula-2, Modula-3, Oberon

14 Language sequences Lisp Algol 60 Algol 68 Pascal ML Modula

15 Functional languages Rooted in logic Lambda calculus, 1930, Alonzo Church LISP John McCarthy Implementation of lambda calculus Meta-Language ML, Rob Milner Functional languages are more appropriate for teaching? Strong typing Program is proof Elements of declarative programming USA

16 History of ML Logic for computable functions (LCF) Robin Milner, Dana Scott Stanford , Edinburgh Meta-language for LCF system Automatization of logic reasoning Proofs Type systems Notation for programs Higher-order functions Programs that search for proof

17 Object-Oriented Languages First OO language is Simula. Simulation programming environment Smalltalk is one of the most famous OO languages Adele Goldberg, Xerox, Palo Alto Everything is object! Every object belongs to one class Class is prototype object Class is object! Complex inheritance hierarchies C++, Java, Objective C,... Java J.Gosling, B.Joy, G.Steele, G.Bracha The Java Language Specification

18 Script languages Web programming languages V zadnjih letih se je pojavila množica jezikov, za delo na Web strežnikih JSP, PhP, JavaScript, ASP, Reseources of Web server System programming languages Strong ties to OS C + Awk, Perl, Python System integration languages

19 High-level languages Information systems 4GL, PL/SQL, SQL3 UML (specifikacije) Electronics VHDL, EDIF,...

20 Prolog Programming in Logic, Robert Kowalski Predicate calculus Horn clauses Unification, resolution Strong, simple and abstract language Back-tracking Declarative and procedural semantics of Prologa Operator CUT (!) Database programming languages Datalog Sicstus, SB Prolog, SWI Prolog,

21 Concepts in programming languages Programming language is programming tool, defined in the form of language, that is used for design and implementation of computer programs. Concepts of programming languages are abstractions used for representation of structure and behaviour of modelled systems.

22 Abstraction From English dictionary Abstraction is description of concept that does not refer to concrete examples Abstraction takes away part of information that relates to concrete Abstraction can mean extraction of substances from raw material The state of someone who is not paying attention Abstraction in philosophy Basic operation of mind Aristotel, St. Thomas Aquinas,...

23 Properties of abstractions in PL Closer to hardware, more simple languages Simple abstractions: Numbers, characters, loops, routines,... Higher abstractions: Objects, modules,... Higher level of abstraction in PL: More directed language Very general abstractions - more specific language General programming language is in the middle: Wide applicability General-purpose PL Very complex languages

24 Abstractions Study of abstractions can improve learning process COMMUNICATIONS OF THE ACM April 2007/Vol. 50, No. 4 IS ABSTRACTION THE KEY TO COMPUTING? Abstractions define language model Imperative languages: variables, loops, procedures,... Funtional languages: funtions Object languages: object and classesi

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26 Concepts in programminng languages Abstractions integrated into language Function, object, method, class, abstract class,... Classification, specialization, aggregation,... Language model Conceptual tool for programming Abstractions define language model Imperative, functional, object-oriented, modular

27 Classifications of PL concepts Algorithmic and data abstractions Algorithmic abstractions Itaration statements, patterns, recursion,... Data abstractions N-tuples, lists, recursive data structures Language and implementation concepts Language abstractions Functions, objects, methods, inheritance Implementation abstractions Memory management, parameter passing

28 Impementation concepts We learn about the implementation of PL constructs Representation of variables, data structures,... Memory management Memory organization Garbage collection Implementation of PL concepts Functions in C, Java, Ocaml,... Parameters in C, Java, Ocaml,... Classes in Java, OCaml,...

29 Why to study concepts in PL? We learn about the possible ways of expressing ideas. We learn how to use given PL abstractions correctly. You have to know the tool It is good to have formal background It is good to have experiences with using tools

30 Meta-Language Meta Language (ML) Developed unintentionally while working on system for automatic theorem proving based on LCF - Logic of computable functions. LCF is a version of lambda calculus Initially at Edinburg University Later in AI group of Stanford University Project leader was Robin Milner. Meta-Language was used as language for expressing mathematical proofs They would change the files with proofs to obtain better proof

31 Meta-Language Success story from functional branch of programming languages Standard ML, SML/NJ, Alice ML, Ocaml, Moscow ML, Mlton, MLKit, SML.NET,... Research related to ML Hindley-Milner type-checking algorithm Polimorfic lambda calculus (System F, Girard)

32 Lambda calculus Lambda calculus is the foundamental formalism for studying programming languages Theory of programming languages Using rule-based reasoning for: deriving expression types, evaluation of expressions, Prooving the properties of language, etc. Static and dynamic semantics of PL Prooving the properties of languages (determinism, strict typing, termination, etc.). Labda calculus is topic of one lecture

33 Objective Caml Objective Caml is reference language Caml core is pure lambda calculus. Theoretically well-studied language. Caml has strong typing. Imperative constructs. Parametric polymorphism Nice object model Modules and functors Ocaml offers more than one programming models Imperative + functional + object-oriented + modular programming model

34 communications of the acm november vo l. 5 4 n o. 1 1

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36 Comparisons of PL Langauge speed The Computer Language Benchmarks Game Speed, size of programs, size of memory used Githut TIOBE Index

37 Language speed J.Mitchel, Lecture, 2005.

38 Popular languages François Labelle, opensource projects of SourceForge 38

39 The Computer Language Benchmarks Game 33 languages, 4 systems, 13 test programs

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41 High-level programming languages can be very efficient Java and Ocaml are efficient languages

42 Speed, size and memory usage of PL 429 programs 13 test programs 33 PL Experiment: Guillaume Marceau

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44 githut Programming languages on github 2M active repositories Parameters No. of projects on github No. of push operations No. of push/repository operations No. of fork operations No. of opened issues No. of watchers 44

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47 TIOBE Indeks: Februar 2015 TIOBE award for programming languages in 2014 JavaScript remains to be very strong Raise of Objective-C finished? Indeks based on: Web search engines: Google, Bing, Yahoo!, Wikipedia, Amazon, YouTube, Baidu TIOBE index is NOT: About best PL About the most used PL 47

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50 Aims of course Concepts of programming languages Language is»conceptual universe (Perlis) Framework for solving problems Usefull concepts and constructs of PLs Learning more than one PL It is good to know the history! Learning concepts from sources Efficient usage of PL constructs 50

51 Methods Lambda calculus Formal foundation Basic principles of procedural PL Lisp: first programming language based on LC ML Mathematical foundations Strong typing Includes most PL constructs Java + C Languages to compare ML! C is still the most popular language Java uses clean object-oriented model Strong typing and dynamic typing 51

52 Methods First classification = language model Functional, imperative, object, module Some concepts will be put forward Functions, parameters, types, scope, control, data abstractions, inheritancem polimorphism, memory We will see diferent approaches Languages used: C, ML, Java Sometimes: Pascal, Fortran, C++, Ada Comparison of PL concepts We know what we can use Concepts can also be very different 52

53 Method Learning about PL constructs and implementation Every construct has its price It always good to know what is happening»below«efficient use of constructs Many times it is neccessary to know implementation of concepts Memory management Representation of data structures Implementation of functions and recursion Dynamic aspects of languages 53

54 What is happening in PL area? Trends: Increased use of strong typing? Classical high-level PL Java, C++, C, C#, Python?,... Increased use of functional languages F#, Erlang, ML, Haskell Script languages JavaScript, Python, Perl, bash Web applications PHP, JSP, ASP System integration Python, Perl 54

55 What is happening in PL area? Trends Java is replacing C and C++? C, C++ is replacing Javo? Lisp/Schema still first language? Practical languages Python in schools? Strong programming environments Strong open-source support 55

56 What is happening in PL area? Research trends Programming languages for target systems Mobile phones, ipad, El.machines, TV, car, washing machine, Concurrent PL Erlang, Concurrent ML, E, CAL,... Dataflow programming Multi-processor, multi-threaded prgramming 56

57 What is happening in PL area? More formal analysis used Type-checking, static and dynamic typing, program analysers, diagnostics, Abstract VM Additional level of abstraction: Virtual Machine Java VM, Erlang VM (BEAM),... Portability Meta-pogramming languages Coq, Isabelle, Twelf Languages used to analyse, test and implement other programming languages 57

58 What to learn? Most commonly used PLs C, C++, Java, Python Concepts of PLs Important implementation ideas New trends New languages: R, VimL, Go, Swift, Scala Functional constructs: Haskell, Ruby, C++, Java Design decisions trade-offs Functional vs. imperative, modular vs. object-oriented,... Current research in the area Parametric types, genericity, types and kinds 58