CS 152: Programming Language Paradigms February 3 Class Meeting Department of Computer Science San Jose State University Spring 2014 Instructor: Ron Mak

CS 152: Programming Language Paradigms

February 3 Class Meeting

Department of Computer ScienceSan Jose State University

Spring 2014Instructor: Ron Mak

www.cs.sjsu.edu/~mak

SJSU Dept. of Computer ScienceSpring 2014: February 3

CS 152: Programming Language Paradigms© R. Mak

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Small Teams

You will learn better by working in small teams.

Form your own teams of 2 or 3 students each.

Choose your team members wisely!

Be sure you’ll be able to meet and communicate with each other and work together well.

After forming a team, no moving to another team.

Each team member will receive the same score on the team assignments.

Email me your team name and the list of team members and email addressesby Monday, February 3: [email protected]_

Use Piazza tofind teammates!



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Team Assignment #1: Algebra 1 Nightmare

Due Monday, February 10 at 11:59 PM

Each team writes a FORTRAN IV program. Get experience writing in a classic programming language. Appreciate the limitations that programmers faced in the 1960s. Understand where today’s languages come from.

Recall the quadratic formula:

a

acbbx

2

42



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Assignment #1, cont’d

The formula produces two complex roots, x1 and x2: (x1real, x1imaginary) and (x2real, x2imaginary)

The discriminant b2 – 4ac determines the nature of the two roots:

Discriminant positive:

a

acbbx

2

42

a

acbbx real 2

42

1

a

acbbx real 2

42

2

021 imaginaryimaginary xx



5



Discriminant zero:

a

bxx realreal 221

021 imaginaryimaginary xx

a

acbbx

2

42



6



Discriminant negative:a

bxx realreal 221

a

acbx imaginary 2

42

1

imaginaryimaginary xx 12

a

acbbx

2

42



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Your FORTRAN program quadratic.for should read the following 21 “punched cards” as input data (text file quadratic.in).

Each card contains one set of values for a, b, and c.

Hint: Use the input format specification 3F10.0 to read the three values from each card.

The 21st card is an “end of deck” marker.

1.0 -2.0 1.01.0 -10.0 25.01.0 -3.0 2.02.0 -6.0 4.01.0 1.0 -2550.010.0 -20.0 10.01000.0 -2000.0 1000.00.02 -0.04 0.021.432 9.876 -4.5678.813 -1.31 0.02.3 1.9917 0.01.0 0.0 -1.01.0 0.0 1.09.0 0.0 36.01.0 2.0 5.0535.0 22.0 1583.0-9.0 23.0 37.061.0 2.0 87.061.0 159.0 87.0100.0 99.0 98.00.0



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For each set of input values a, b, and c, use the quadratic formula to compute the two roots x1 and x2. Compute the quadratic formula in a FORTRAN subroutine.

For each set of input values, your program should output the values of a, b, c, x1real, x1imaginary, x2real, and x2imaginary. Also print the card count.

Hint: Use the format specification 1PE15.4 to output each real number. You can specify a repeat factor such as 1P3E15.4. The E means exponential notation, and the 1P moves the decimal point to the right by one (e.g., print -2.5500E+03 instead of the default -0.2550E+04)_



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Sample output. Note the blanked out items in the last four columns

for values that are purely real or purely imaginary. COUNT A B C X1 REAL X1 IMG X2 REAL X2 IMG

1: 1.0000E+00 -2.0000E+00 1.0000E+00 1.0000E+00 1.0000E+00 2: 1.0000E+00 -1.0000E+01 2.5000E+01 5.0000E+00 5.0000E+00 3: 1.0000E+00 -3.0000E+00 2.0000E+00 2.0000E+00 1.0000E+00 4: 2.0000E+00 -6.0000E+00 4.0000E+00 2.0000E+00 1.0000E+00 5: 1.0000E+00 1.0000E+00 -2.5500E+03 5.0000E+01 -5.1000E+01 6: 1.0000E+01 -2.0000E+01 1.0000E+01 1.0000E+00 1.0000E+00 7: 1.0000E+03 -2.0000E+03 1.0000E+03 1.0000E+00 1.0000E+00 8: 2.0000E-02 -4.0000E-02 2.0000E-02 1.0000E+00 1.0000E+00 9: 1.4320E+00 9.8760E+00 -4.5670E+00 4.3500E-01 -7.3316E+00 10: 8.8130E+00 -1.3100E+00 0.0000E+00 1.4864E-01 0.0000E+00 11: 2.3000E+00 1.9917E+00 0.0000E+00 0.0000E+00 -8.6596E-01 12: 1.0000E+00 0.0000E+00 -1.0000E+00 1.0000E+00 -1.0000E+00 13: 1.0000E+00 0.0000E+00 1.0000E+00 1.0000E+00 -1.0000E+00 14: 9.0000E+00 0.0000E+00 3.6000E+01 2.0000E+00 -2.0000E+00 15: 1.0000E+00 2.0000E+00 5.0000E+00 -1.0000E+00 2.0000E+00 -1.0000E+00 -2.0000E+00 16: 5.3500E+02 2.2000E+01 1.5830E+03 -2.0561E-02 1.7200E+00 -2.0561E-02 -1.7200E+00 17: -9.0000E+00 2.3000E+01 3.7000E+01 -1.1189E+00 3.6744E+00 18: 6.1000E+01 2.0000E+00 8.7000E+01 -1.6393E-02 1.1941E+00 -1.6393E-02 -1.1941E+00 19: 6.1000E+01 1.5900E+02 8.7000E+01 -7.8145E-01 -1.8251E+00 20: 1.0000E+02 9.9000E+01 9.8000E+01 -4.9500E-01 8.5731E-01 -4.9500E-01 -8.5731E-01

END OF PROGRAM: 20 CARDS READ.



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Do not use modern FORTRAN features. Use only FORTRAN IV (also known as FORTRAN 66). A short reference:

http://www.math-cs.gordon.edu/courses/cps323/FORTRAN/fortran.html

A “C” in column 1 is for a comment. Statement numbers are restricted to

columns 1 through 5. Statements are in columns 7 through 72. A non-blank character in column 6 means what follows

is a continuation of the previous line. Keep your statements short and column 6 is always blank.

_



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There were no lower-case characters with punched cards, so everything is in upper case.

Variable names are limited to 6 characters.

You can declare variables with the INTEGER, REAL, DOUBLE PRECISION, and LOGICAL (boolean) statements. Example: INTEGER I, J, K

However, variable declarations are optional! By default, any variable that starts with the letters I through N are type integer, and the rest are type real. You still have to declare DOUBLE PRECISION and LOGICAL variables.



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The LOGICAL values are .TRUE. and .FALSE. (note the surrounding periods).

The relational operators are: .EQ. .NE. .LT. .LE. GT. .GE. .NOT. .AND. .OR. (more surrounding periods).



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There are two types of IF statements, the logical IF and the arithmetic IF.

The logical IF tests a logical (boolean) expression. You can have only one statement as the true part.

There is no else part. Examples:

IF (A .GT. B) A = 3.2 IF ((A .LE. B) .AND. (C .NE. 0.0)) GO TO 7

The arithmetic IF tests an arithmetic expression. Guess how the arithmetic IF works. Example: IF (A-B) 110, 201, 3



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There is also the computed GO TO statement, the precursor to the select or case statement in today's languages. Guess how this example works:

GO TO (43, 182, 672, 12, 8), K

You will undoubtedly stumble unto some unexpected syntax limitations. Remember, this is a nearly 60 years old language!



15


Windows

Download the Open Watcom FORTRAN development environment:http://www.openwatcom.org/index.php/Main_Page

It implements FORTRAN 77, which is backwards compatible with FORTRAN IV._



16


Mac

First, you must get gcc (the GNU C compiler) by downloading and installing the command-line tools for Xcode: http://www.mkyong.com/mac/how-to-install-gcc-compiler-on-mac-os-x/

Next, download g77-intel-bin.tar.gz (g77 3.4) from http://hpc.sourceforge.net/. It will install the FORTRAN compiler into /usr/local.

Then you should then be able to compile and run with the commands

g77 -o quadratic quadratic.for./quadratic < quadratic.in



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This is a team assignment. Each team turns in one assignment. Each member of the team will get the same score.

Email the source of the FORTRAN program and the text output to [email protected].

Subject line: CS 152 Assignment #1, team name Example: CS 152 Assignment #1, SuperCoders

Be sure to cc all members of your team so that when I send you your score, I can just do a “Reply all”._



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Programming Language Abstractions

Two types of programming language abstractions: Data abstraction Control abstraction

Data abstractions Simplify the behavior and attributes of data. Examples: numbers, character strings, search trees

Control abstractions Simplify properties of the transfer of control. Examples: loops, conditional statements, procedure calls

_



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Programming Language Abstractions, cont’d

Abstractions can also be categorized by levels. How much information is contained or hidden

in the abstraction? An orthogonal axis to data and control.

Basic abstractions Collect the most localized machine information.

Structured abstractions Collect intermediate information about

the structure of a program.

Unit abstractions Collect large-scale information in a program.



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Programming Language Abstractions, cont’d

data control

basic

structured

unit

basic data

structured data

unit data

basic control

structured control

unit control

TYPE

LEV

EL



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Basic Data Abstractions

Hide the internal representation of common data values. Values are also called “primitive” or “atomic”. The programmer normally cannot access the component parts or

bits of the internal representation.

Variables Symbolic names hide computer memory locations

containing data values.

Data types Names given to kinds of data values. Determine the valid operations on the data values.

Declarations Give variables their names and specify their data types.

_



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Structured Data Abstractions

Data structure Collects related data values into a single entity. Hides component parts. Parts can be accessed and modified.

Examples: An array is a sequence of individually indexed items

(all the same data type). An employee record contains name, address, phone, salary

(different data types). A text file is a sequence of characters transferred

to and from an external storage device._



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Unit Data Abstractions

Abstract data type (ADT) A set of data values and the operations on those values. Information hiding: How the values are stored and how the

operations are implemented.

Separate the interface from the implementation. Interface: The set of operations available to the user Implementation: The internal representation of the data values

and their operations.

Examples Java package Python module



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Unit Data Abstractions, cont’d

Data unit abstraction also provides reusability.

Typically, components are entered into a library. Applications can combine components into larger entities. Interoperability allows different applications

to share components.

An application programming interface (API) gives information about a library’s components._



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Basic Control Abstractions

Statements that combine a few machine instructions into an abstract statement that is easier to understand.

Example: sum = first + second What is abstracted away?

Syntactic sugar allows you to replace some notation with a simpler, shorthand notation.

Example: x += 10replaces: x = x + 10_



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Structured Control Abstractions

Divide a program into groups of instructions nested within tests that govern their execution.

Express the logic of primary control structures of sequencing, selection, and iteration._



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Structured Control Abstractions, cont’d

Example: A Java for loop operating on an array:

Use of an iterator and the syntactic sugar of a Java enhanced for loop:



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Structured Control Abstractions, cont’d

Procedures AKA subroutines, subprograms

Functions Procedures that return values

Higher-order functions Functions that can accept other functions as arguments

and return functions as values. Combine functions into higher-level abstractions. Example: The Lisp map and reduce functions:

(reduce + (map abs (list 33 -10 66 68 -4)))

(33 10 66 68 4)

201

(map abs (list 33 -10 66 68 -4))



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Unit Control Abstractions

Unit A standalone collection of procedures. Provides logically related services to other parts of a program. Allows a program to be understood as a whole.

Don’t need to know the details of the services provided by the unit.

Threads Separately executed control paths within the Java system. Threads must be synchronized.

Processes Other programs executing outside the Java system. Interprocess communication Process synchronization

_



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Computational Paradigms

Paradigm: a pattern or model

Imperative paradigm Instructions executed sequentially. Variables represent memory locations. Assignment statements change the values of variables.

The von Neumann bottleneck A program must be described as a sequence of instructions. Restricts the ability of a programming language to provide:

parallel computation nondeterministic computation (does not depend on order)

_



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Computational Paradigms

Functional paradigm Based on the abstract notion of a function in the

lambda calculus.

Logic paradigm Based on symbolic logic.

Both functional and logic paradigms correspond to mathematical foundations. Easier to determine if a program will execute correctly.

Object-oriented paradigm Reusable code that operates in a way that

mimic the behaviors of real-world objects.



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Language Definition

How can we formally define a programming language?

Grammar What sequence of characters is correct within the language? Examples: What are valid expressions?

Assignment statements? If statements? How can we specify the language’s syntax.

Meaning and behavior What does an assignment statement mean? How does an if statement behave at run time? How can we specify the language’s semantics.

_



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Language Definition

Formal language definition allows you to:

Reason mathematically about programs.

Promote standardization for machine or implementation independence.

Define program behavior and interaction.

Ensure discipline when a language is designed._



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Language Syntax

Grammar: The formal definition of a language’s syntax. Similar to the grammar of a natural language. Precisely specifies what are valid constructs in the language.

Tokens: Elements of the language identifiers numbers reserved words: if else for while do etc. special symbols: + - = ( ) >= etc.

Lexical structure Similar to spelling rules in a natural language. The rules that define what are valid language tokens.



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Language Syntax

Example: Syntax of the Java if statement:

This syntax rule is written in English. Later, we’ll use a more precise notation called

Backus Naur Form (BNF)._

An if statement consists of the reserved word iffollowed by a left parenthesis followed by anexpression followed by a right parenthesisfollowed by a statement. Optionally, this is

followed by the else part which consists of thereserved word else followed by a statement.



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Language Semantics

Semantics: The meaning of a language’s statements. What is the effect of executing the statement at run time? It can be difficult to provide a comprehensive description

of meaning in all contexts.

Example: Semantics of the Java if statement:

First evaluate the expression following thereserved word if. If the expression’s value is true,

then execute the statement following the expression,otherwise skip over the statement. If there is anelse part, execute the statement following the

reserved word else if the expression’s value is false,otherwise skip over that statement.



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Language Semantics

There isn’t a generally accepted formal method for describing semantics.

Several notational systems have been developed:

Operational semantics Denotational semantics Axiomatic semantics

_



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Syntax and Semantics

How are a language’s syntax and semantics used?

A well-specified syntax allows programs in the language to be automatically read and translated.

Well-understood semantics allows the program to be translated into a equivalent program. Equivalent programs have similar runtime behaviors.

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Documents

CS 152: Programming Language Paradigms February 3 Class Meeting Department of Computer Science San Jose State University Spring 2014 Instructor: Ron Mak