6/27/2015G. Levine1 PROGRAMMING LANGUAGES Text: Programming Languages, Design and Implementation Pratt and Zelkowitz 4 th ed. Prentice-Hall

6/27/2015G. Levine2 Introduction Concepts underlying all computer programming  Assist in learning new languages  Assist in understanding current languages  Efficiency, reliability considerations  Design and reuse considerations  Implementation details G. Levine  

6/27/2015G. Levine3 Topics of Discussion History of development of programming languages Development of specific language features Language implementation/environment Language features Programming in specific languages

6/27/2015G. Levine4 Language Paradigms Imperative/ procedural languages  Assignment statement is chief characteristic – places value in CELL  consider x = x *x + 1 Functional/ applicative languages  (sum (times (x x) 1)) not placed in x Rule-based / logic programming Object-oriented programming  Imperative style in the small  Module communication similar to applicative languages Concurrent programming  Need for synchronization

6/27/2015G. Levine5 History of Programming Languages 1 st generation – machine language  Octal representation of  op code  operand (s) – memory or register cells 2 nd generation- assembly language  Symbolic op codes, operands  Translated by assembler to machine language  Delay in binding from writing to translating time of symbolic name to machine address

6/27/2015G. Levine6 1 st and 2 nd generation languages continued Problems  Not portable- specific to hardware  Difficult to read, i.e., maintain  Consider as an instruction  Difficult to write (see above)  Lack of structures in machine language  Data- support for arrays (block memory) Array looping with self modifying code  Control - conditional and jump (goto) Some reuse already existed –  Programmers shared debugged i/o and mathematical routines

6/27/2015G. Levine7 Beginning of 3 rd generation languages Grace Hopper- early 1950s A-O, B-O  use of subroutines  scientific (military uses) Lack of hardware support

6/27/2015G. Levine8 FORTRAN I(Backus & team) History – see   Goals  Efficiency (still valid)  Formula translation – scientific applications  Research Contributions  Expressions (precendence rules,.GT., etc.)  Multidimensional array manipulation  Do loops  IBM704- index registers, keyboard included +, /, *

6/27/2015G. Levine9 Early FORTRAN – disadvantages Concern for storage – use of equivalence, etc. Fixed format; no reserved words; blanks ignored Implicit typing Spaghetti code Loop and conditional hard to distinguish No record type

6/27/2015G. Levine10 Obsolete example from Fortran Do loop test at bottom at loop Do 10 I = M, A (I) = 5 If M > 0 this still executed once. G.L. Assembler: Load I5 register1 (R1) LOOPStore 5 Array DecR1 BZR1OUT Inc LOOP JmpLOOP OUT

6/27/2015G. Levine11 Another obsolete example from FORTRAN Equivalence (A, B) Dimension A(100), B(100) Real A, B  overlay Or Dimension A(100), B(50) Real A, Complex B  alias

6/27/2015G. Levine12 Why FORTRAN was successful? Evolved: Fortran II, IV, 77, 90  Upward compatibility Portability  Compiled languages can be machine independent – role of standardization Efficiency  Array manipulation  Static storage allocation Support for numeric applications  Complex numbers as primitive data type Strong support from IBM

6/27/2015G. Levine13 LISP (List Processing McCarthy ) Functional language Symbolic applications (A.I.) Recursion and conditional as control structures List as primitive data structure Garbage collection

6/27/2015G. Levine14 ALGOL (Backus + team) ) Algorithmic language  Free format  Structured control  Sequence, conditional, loop  Blocks (scope rules)  stack storage allocation (recursion)  Own (static) variables  BNF – meta language to precisely define a language I/O not defined – NOT PORTABLE

6/27/2015G. Levine15 COBOL –1960s Business Applications Fixed Format Stress on data structures  Data division  Record type  Fixed point type “circles” of compilers for advanced business capabilities Toc Toc

6/27/2015G. Levine16 Example from COBOL Data defined by bytes  Great for portability  (note that C’s int type may be implemented by 16 or 32 bits)  Need to save storage. 01 Date. 05 Month pic Date pic Year pic 99. – y2K  This feature was an option in PL/1

6/27/2015G. Levine17 Why COBOL was (is) successful? DoD Support Easy to read  Self documenting Fairly easy to write  English type statements  (perform 5 times) Great data support  Interface to databases

6/27/2015G. Levine18 Other languages PL/1- late 60s – all purpose language – pointers, exception handling Simula67- simulation language- classes and coroutines Smalltalk –late 1970s- object oriented; entire programming environment C s – system programming (UNIX)  Small, efficient, Bell Labs support Ada83 – software engineering principles C s object oriented C Java – 1990s – for the Internet 4GLs and script languages

6/27/2015G. Levine19 Environments Early batch systems  Efficiency of time and space Time-sharing systems  User Friendliness  Interactive I/O PC and the Internet  Graphical features Embedded systems  Time constraints (hard real time)  Parallel activities  Error control  Reliability

6/27/2015G. Levine20 What should we look for in a language? Research contributions Strengths, weaknesses  Specific or general applications Support of Control abstraction Support of Data abstraction Support of Reuse  Modification/ maintainability  Portability  Generality Efficiency  Compiled or interpreted

6/27/2015G. Levine21 Syntax and Semantics Syntax – rules of the language  first compiler phase is parsing, which determines whether module is a valid string of the language Semantics- what goes into the cells and when We’ll see many examples of different ways that syntax can be interpreted  Ex: parameter passing Orthogonality – whether valid syntactic elements can be combined  Ex: a file cannot be a value parameter in Pascal