Programming Language Design Chapter 1

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Programming Language DesignChapter 1

• CS 350 Programming Language Design
• Indiana University Purdue University Fort Wayne

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Chapter 1 Preliminaries

• Reasons for Studying Programming Languages
• Programming Domains
• Language Evaluation Criteria
• Influences on Language Design
• Language Categories
• Language Design Trade-Offs
• Implementation Methods
• Programming Environments

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Reasons for Studying Programming Languages

• The expressive power of the language we use to
  communicate influences the depth at which we can
  think
• It is difficult to conceptualize structures you
  cannot describe
• Consider implementing a complex application in
  assembly language
• without knowledge of subprograms or
  object-oriented programming?
• with that knowledge?

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Reasons for Studying Programming Languages

• Ability to choose the best language for the
  problem
• Popular languages used today are far from ideal
• Is a cheap compiler a good reason for choosing a
  language?
• Is programmer familiarity with a related language
  a good reason for choosing a language?
• Foundation for learning new languages

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Reasons for Studying Programming Languages

• Understanding of runtime and implementation
  issues
• Relative efficiency of alternative constructs
• Common bugs
• Proper use of a language
• Overall advancement of computing

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Programming Domains

• Scientific applications
• Large number of floating point computations
• Examples Mathematica and Maple
• Business applications
• Produce reports
• Use decimal numbers and characters
• COBOL

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Programming Domains

• Artificial intelligence
• Symbols rather than numbers are typically
  manipulated
• First AI language was LISP McCarthy
• Prolog Clocksin and Mellish
• Systems programming
• Need for efficiency because of continuous use
• Low-level features for interfaces to external
  devices
• C

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Programming Domains

• Web software
• Markup languages
• Such as XHTML
• Scripting languages
• A list of commands is placed in a file or in
  XHTML document for execution
• Perl, JavaScript, PHP
• Special-purpose languages
• RPG business reports
• APT programmable machine tools
• GPSS simulation

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Language Evaluation Criteria

• Readability
• Writability
• Reliability
• Cost
• Other

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Language Evaluation Criteria

• Readability
• Very important
• Maintenance can be 70 90 of system lifecycle
  cost
• Overall simplicity
• Too many features are bad
• Multiplicity of features is bad
• Are you confused by Java I/O choices?

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Language Evaluation Criteria

• Readability
• Orthogonality
• A relatively small set of primitive constructs
  that can be combined in a relatively small number
  of ways
• Consistent set of rules for combining constructs
  (simplicity)
• Every possible combination is legal
• Makes the language easy to learn and read
• Meaning is context independent
• VAX assembly language and Ada are good examples
• Lack of orthogonality leads to exceptions to
  rules
• C is littered with special cases
• E.g. - structs can be returned from functions but
  arrays cannot

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Language Evaluation Criteria

• Readability
• Useful control statements
• Ability to define data types and structures
• Syntax considerations
• Provision for descriptive identifiers
• BASIC once allowed only identifiers to consist of
  one character with an optional digit
• Meaningful reserved words
• Meaning should flow from appearance

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Language Evaluation Criteria

• Writability
• Most readability factors also apply to
  writability
• Simplicity and orthogonality
• Control statements, data types and structures
• Support for abstraction
• Data abstraction
• Process abstraction
• Expressivity
• It is easy to express program ideas in the
  language
• APL is a good example

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Language Evaluation Criteria

• Reliability
• Type checking
• Famous failure of space shuttle experiment due to
  int / float mix-up in parameter passing
• Exception handling
• Ability to intercept run-time errors
• Aliasing
• Ability to use different names to reference the
  same memory
• A dangerous feature
• Readability and writability both influence
  reliability

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Language Evaluation Criteria

• Cost
• Training programmers to use language
• Writing programs in a particular problem domain
• Compiling programs
• Executing programs
• Language implementation system (free?)
• Reliability
• Maintaining programs
• Others portability, generality, well-definedness

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Von Neumann computer architecture
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Influences on Language Design

• We use imperative languages, at least in part,
  because we use von Neumann machines
• Data and programs stored in same memory
• Memory is separate from CPU
• Instructions and data are piped from memory to
  CPU
• Basis for imperative languages
• Variables model memory cells
• Assignment statements model piping
• Iteration is the most efficient way to implement
  repetition

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Influences on Language Design

• Programming methodologies
• 1950s and early 1960s
• Simple applications
• Overriding concern about machine efficiency
• Late 1960s
• People efficiency became important
• Readability
• Better control structures
• Structured programming
• Top-down design and step-wise refinement

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Influences on Language Design

• Programming methodologies
• Late 1970s
• Process-oriented techniques yielded to
  data-oriented techniques
• Data abstraction
• Middle 1980s to present
• Object-oriented programming
• Encapsulation with data abstraction
• Inheritance
• Dynamic method binding
• Smalltalk and Java
• Concurrent programming and parallelism
• Creating and controlling concurrent program units

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Language Categories

• Imperative
• Central features
• Variables
• Assignment statements
• Iteration
• Algorithm specified in detail with a specific
  order of execution for statements
• C, Pascal, Visual BASIC.NET
• Functional
• Main means of making computations is by applying
  functions to given parameters
• No variables
• No looping
• LISP, Scheme

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Language Categories

• Logic
• Rule-based
• Rules are specified in no special order
• Language system chooses execution order that
  produces the desired result
• Prolog
• Object-oriented
• Encapsulate data objects with processing
• Inheritance and dynamic type binding
• Grew out of imperative languages
• Smalltalk, C, Java

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Language Design Trade-Offs

• Designing a programming language involves an
  number of compromises and trade-offs
• Reliability vs. cost of execution
• Range checking for array references?
• Readability vs. writability
• The APL language traded readability for
  writability
• Writability vs. reliability
• Pascal variant records are flexible but not safe
• C pointers are flexible but not safe

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Layered View of Computer
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Implementation Methods

• Compilation
• Translates a high-level program to machine code
• Slow translation
• Fast execution
• Separate compilation units must be combined by a
  linker into an executable image
• (.exe file)

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Implementation Methods

• Pure interpretation
• No translation before execution
• Slow execution
• Loop statements are repeatedly translated
• Becoming rare except for web scripting languages
• JavaScript
• PHP

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Implementation Methods

• Hybrid implementation systems
• Translates a high-level language to intermediate
  code
• Each statement is translated only once in
  contrast to pure interpretation
• Medium execution speed
• Smalltalk and Java
• Intermediate code is called bytecode
• The interpreter is the JVM
• JIT technology now widely used with Java and .NET

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Programming Environments

• The collection of tools used in software
  development
• File system, text editor, compiler, linker
• Borland JBuilder
• An integrated development environment for Java
• Microsoft Visual Studio.NET
• A large, complex visual environment
• Used to program in C, Visual BASIC.NET, Jscript,
  J, and C