CSE%203302CSE@UTA

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CSE3302Programming Languages(notes, notes,
notes)

• Dr. Carter Tiernan

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Block Structured Languages Activation records

• Fixed program part
• Variable activation-record part
• Instruction part
• Environment part
• Local context
• Nonlocal context

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Nonlocal context

• Static link
• IP-EP locus of control
• Two coordinate access
• Static distance
• Offset
• Two step access

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Procedure Activation

• Needs static and dynamic links
• Three steps
• Save caller state
• Create callee activation record
• Enter callee in context of new record

Procedure Deactivation

• Two steps
• Delete callee activation record
• Restore the state of the caller

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Procedural Parameters

• Two element record
• IP gives entry address of actual procedure
• EP gives pointer to environment of definition of
  procedure
• Block structured languages generally only allow
  procedures to be passed in - not to be returned

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Nonlocal context

• Static chains as discussed
• Implemented as linked lists
• Display
• Random access to context
• Array with pointers to activation records
• Calls require saving display data
• Shallow binding
• Static activation records on stack

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Blocks

• Handled like degenerate procedures

Concepts

• Activation records very important in language
  implementation
• Two-coordinate addressing is also significant

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Ada Overview

• Rationale
• Software complexity and cost
• Maintenance and portability
• Government backing
• History
• 1975 - 79 Specifications
• CII-Honeywell-Bull Jean Ichbiah
• Mil std and ANSI 83, ISO 87

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Ada Highlights

• Abstract Data Types
• Information Hiding (D. L. Parnas)
• Verification
• Concurrency
• Generally uses Pascal as basis

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Ada

• Packages support info hiding and implement
  abstract data types
• Specification of public names
• Private body of package
• Control structures include
• Exception handling
• Concurrent programming

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Ada Declarations

• Object (constants and variables)
• Type
• Subprogram (procedures, functions and overloaded
  operators)
• Package (executable modules)
• Task (concurrently executable modules)

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Ada Data Structures

• Based on Pascal
• Range constraints
• Accuracy constraints digits, delta
• Discriminant constraint
• Index constraint
• Name equivalence
• Subtype, derived type
• Overloaded enumerations

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Ada Name structures

• Variables can be initialized at declaration
• Constants are declared with keyword and are
  constant within scope
• Separation of interface implementation

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Ada Issues

• Global Variables Considered Harmful Wulf Shaw
• Side effects
• Indiscriminate access
• Vulnerability
• No overlapping definitions
• Parnass principles of information hiding
• One must provide the intended user with all the
  info needed to use the module correctly and
  nothing more.
• One must provide the implementor with all the
  info needed to complete the module and nothing
  more.

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Name structures (cont.)

• Packages
• Interface specification
• public part of package
• May have private section
• Body
• Defines everything in interface specification
• This is private to the package developer
• Use ltpackage_namegt
• With ltpackage_namegt

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Ada Packages

• ADT
• Library of routines
• Shared data structure
• Generic packages
• ADT templates
• Parameters
• Internal vs. External representations

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Ada Control Structures

• Iterator - loop ltbodygt end loop
• Infinite loop - uses exit keyword or exit
  when
• while phrase prefix
• for phrase prefix
• Conditional - if ltconditiongtthen ltbodygtend if
• Case
• Subprograms
• Goto
• Exception handling
• Concurrency control

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4th Generation Languages
4th

• Data abstraction languages
• Control structure for concurrency
• Refinement and correction of 3rd gen