Ada, Scheme, REmory Wingard

Ada

History• Department of Defense in search of high

level language around 1975.

• Requirements drafted for the language.

• Competition between vendors to produce language narrowed down to four.

• Cii-Honeywell/Bull's language design won.(1979)

History cont.

• Large requirements called for a large language.

• Was not released to the public during testing.

• Dr. Jean Ichbiah headed the French team

• Based on Pascal

The Compiler

• Compilers for Ada were not developed until four years after the language was completed.

• Compilers are trademarked.

• Slow compile-time and run-time performance in the beginning.

Versions

• Original: Ada 83

• Ada 95

• Ada 2005

• Current version: Ada 2012

Usage

• Embedded systems

• Modern principles of software engineering

• Large software systems

Structure of programs

• Programs composed of program units

• Program units have subprograms, packages, task units, protected units, and generic units.

• Units consist of two parts: specifications and the body

• Most can be compiled separately

Subprograms

• Used to express algorithms

• Two kinds: procedures and functions

• Procedure is a way to bring up actions

• Functions provide computation of a value.

Packages• Considered the highlight of Ada

• Program units that encapsulate a group of related declarations and control visibility.

• Supports definition of interfaces and implementations

• Information hiding and abstract data types

• Structure for larger systems

Exception Handling

• Based on PL/I and CLU

• Handled locally in the code so reference environment is the same.

• Inadequate for task.

• No extension to Ada 95 for exception handling.

Types

• Integer

• Character

• Boolean

• Float

• String

*Considered to be strongly typed*

• Readability?

• Writability?

• Cost?

RFunctional, Statistical Computing, Graphics, Data

Analysis

History

• Implementation of the S programming language

• Created by Ross Ihaka and Robert Gentleman

Advantages

• Open sourced

• Available across multiple platforms

• Ease of design of graphics

• Data analysis

Packages• Stores data sets and functions.

• Similar to classes in Java

• Functions in packages are related

• Large number of packages for many different purposes

• Only a handful loaded by default

Commands• Two forms: expressions assignments

• Expression are printed immediately, values are not stored

• Assignments pass values to variables, these results are not printed

• Commands can be grouped by braces

• Separation of commands done by semi-colons

expression/assignment examples

Objects

• Numeric vectors, character vectors, lists, functions

• Actually everything in R are objects

• example

Constants

• Building blocks for data objects

• Numbers, character values, and symbols

• examples.

Precedence rules• function calls and grouping expressions

• Index and lookup operators

• Arithmetic

• Comparison

• Formulas

• Assignment

• Help

Control Structures

• Conditional Statements

if (condition) true_expression else false_expression

Scheme

Overview

• Developed in the 70s at MIT

• An extension of LISP

• Uses: optimizing compilers, financial analysis packages, operating systems, and writing text editiors

The Interpreter

• Interactive

• Infinite read-evaluate-print loop

• Very small, increased reliability

Programs• Collection of functional definitions

• DEFINE

• binds names to a value

• binds names to lambda expressions

• prototypes

• expression

Programs cont.• Block structured

• keywords and variables are lexically scoped

• This makes the programs modular

• Increases readability and reliability

• Maintenance is easier

Programs cont.

• Scope of binding determined before evaluation of program by compiler

• Makes the code more efficient

Arithmetic

• Scheme uses prefix notation

• This simplifies precedence and associativity of operators

• example

Data Structures• Scheme uses lists rather than arrays

• Shown as sequences of objects surrounded by parenthesis.

• quote is used to tell the program that the list is to be treated as data and not a procedure

• List manipulation:

• car- returns the first element in a list

• cdr- returns the rest of the list

• cons- used to construct list

Advantages

• Portable

• Used to teach programming in high schools

• Very small and simplistic