chapter one: metrics and influences on language design lesson 02

Chapter One: Metrics and Influences on Language Design

Lesson 02

04/19/23Programming Languages: lecture two

2

Language Evaluation Criteria


3

Readability Writability Reliability Cost

A language that has poor readability, writability, and/or reliability has a high cost

A language that has poor readability, writability, and/or reliability has a high cost

Example writable vs. readable:

APL has a powerful set of operators for array operands. Can be used to create very complex, very long expressions.

APL has excellent writability

APL has poor readability

Example writable vs. readable:

APL has a powerful set of operators for array operands. Can be used to create very complex, very long expressions.

APL has excellent writability

APL has poor readability

Reliable if programs that are written in the language tend to be error free. Readability and writability contribute to reliability

Example: people tend to make mistakes when using pointers which leads to unreliable programs

Reliable if programs that are written in the language tend to be error free. Readability and writability contribute to reliability

Example: people tend to make mistakes when using pointers which leads to unreliable programs

Characteristics that affect criteria


4

To be writable, should be readable (if ever need to make changes to code)

To be reliable, must be readable and writable

How could APL be writable but not readable?

How could APL be writable but not readable?

Readability


5

Overall simplicity Small number of features and constructs Minimal feature multiplicity (multiple ways to

do things, a++, a+=1,a=a+1) Minimal operator overloading

Orthogonality Few exceptions to the rules, always behaves

as expected Data types

Adequate predefined data types (example: int used because no boolean)

Syntax considerations Allowable Identifiers (another word for a

variable) Intuitive meaning of statements

Writability


6

Support for abstraction Expressivity

A set of relatively convenient ways of specifying operations (++, vector multiplication, for vs. while)

Strength and number of operators and predefined functions

Let’s try it


7

A programming language that has a relatively small number of features and constructs, has seemingly adequate predefined data types, statements and constructs that are intuitive, but has little support for abstracting the data types or for performing commonly occurring operations needed in the target programming domain, is ____________.

Readable, writable, both, or neither?

A programming language that has an relatively small number of features and constructs, has a large number predefined data types tailored for use in a particular programming domain, statements and constructs that are not very intuitive but that are extremely powerful and complex when employed within the target programming domain , is ____________.

Readable, writable, both, or neither?

Reliability


8

Type checking Exception handling Disallow aliasing

(two variables pointing to same object)

Cost


9

Readability/writability Training programmers to use the language Support for design approach and

problem domain (object orientation, easy integration of appropriate math operations, etc.)

Maintaining programs, the more readable the better

Reliability Constant debugging

Literal cost Actual cost of compiler software (free?) Compile time Execution efficiency

Two Major Influences on Language Design


10

Computer Architecture Programming Methodologies

Software Design and Engineering Approaches

John von Neumann: von Neumann Architecture


11

Mathematician Member of the Manhattan

Project Same memory for

program and data

First programming languages…


12

1’s and 0’s (Machine Language) Designed to navigate the existing architecture

Machine language: 10110000 01100001

Move the value 61h (or 97 decimal; the h-suffix means hexadecimal; into the processor register named "AL".

Machine language: 10110000 01100001


ENIACArtillery firing tables: World War II

Artillery firing tables: World War II

First compiled languages…


13

Assembly: directly translates to machine language one to one correspondence between commands in

machine and assembly languages

Textual, so easier to remember

Machine language: 10110000 01100001Assembly: MOV AL, 61h


Machine language: 10110000 01100001Assembly: MOV AL, 61h


IBM 360

Finally, high-level, compiled programs


14

Make human readable mov ax, acmp ax, bjne ElseBlkmov ax, dmov c, ax jmp EndOfIf

ElseBlk: inc b

EndOfIf:

if (a=b) then c := d

else b := b + 1;

Course is generally about the …


15

Evolution of high-level, compiled languages

Text (source)

0101010101010101010010(machine language)

What other kinds of languages are there (besides compiled)?

• Interpreted: on the fly determination of program meaning

• Hybrid: when execute makes a pass compiling to an intermediate form

• JIT: (just in time) subprograms compiled into machine code when they are called

Architecture first, later programming methodologies


16

Mid 1950s to early 1960s: machine efficiency Late 50’s: application to problems in artificial

intelligence Late 1960s: People efficiency became important;

readability, better control structures and modularity structured programming top-down design and step-wise refinement

Late 1970s: Process-oriented to data-oriented data abstraction – data structures

Middle 1980s: Object-oriented programming Data abstraction + inheritance + polymorphism

If/else condition checking and loops

Control Structures?

First high-level languages…


17

Considered to be “imperative” Central features are variables,

assignment statements, and iteration

Include languages that support object-oriented programming

Include scripting languages Include the visual languages Examples: C, Java, Perl, JavaScript,

Visual BASIC .NET, C++

Why imperative?


18

Architecture driven Pull data and instructions from memory Sequential operations clock driven

Also mindset driven: Definition of an algorithm

A step-by-step procedure for solving a problem in a finite number of steps

A limitation to early imperative languages


19

When study languages Must formalize definitions Many definitions and proofs (inductive)

are recursive in nature Doesn’t take long when studying

algorithms to move into the realm of recursion Recurrence relations

Earliest high-level compiled languages (Fortran) could not handle recursion

The Search for Artificial Intelligence


20

Shortly after first high-level languages (Mid 50’s) … Allen Newell, J. C. Shaw, and

Herbert Simon “The Logical Theorist”

Used a program to actually prove theorems

Approach called “list processing”

Artificial Intelligence (List Processing)


21

Proof technique Based upon a search tree: the

root was the initial hypothesis, each branch was a deduction based on the rules of logic.

Required recursion to elegantly solve the tree search

Method needed for processing symbolic data in linked lists

Came up with own language: Information Processing Language (IPL) for list processing Never took off: too low-level,

essentially assembly language

Retrofit list processing


22

IBM retrofitted list processing to the first high-level programming language: Fortran (Fortran List Processing Language or FLPL)

John McCarthy of MIT worked for a summer at IBM Studied symbolic

differentiation Concluded that list processing

required recursion, condition checking, and implicit deallocation of abandoned lists

FLPL did not have xkcd.com

LISP


23

McCarthy and Minsky of MIT therefore developed LISP (List Programming Language)

Approach became known as functional programming

Each list has as first item a function, all subsequent items are arguments

Second major category of programming languages (first being imperative)

(f, i1, i2, …, in)

Function applied to items in the list

Example

04/19/23Genealogy of Common Languages24

Factorial mathematical definition

In LISP

0 if )1(*

0 if 1)(

nnfn

nnf

(DEFINE (factorial n) (IF (= n 0) 1 (* n (factorial (- n 1)))))

In short: functional languages…


25

Were the result of the vacuum left by early languages when they did not support recursion Virtually all “imperative” programming languages now support

recursion, linked lists, and passing of functions as arguments Hasn’t really received widespread acceptance

Most list processing languages are interpreted (can be slow) Most users find it difficult to master: many of us think

“imperatively” (i.e. step-by-step) when we think of algorithms

AI strikes again


26

Early 70’s: it became apparent that much of AI was comprised of logic based conclusions Predicate calculus (if a is true then b must be

true) Inference process

Example It can be deduced that X is the grandparent

of Z if it si true that X is the parent of Y and Y is the parent of Z

Can query a database of fact statements and rules Like Y is the parent of Z Looking for relationships that satisfy rule

statements like grandparent relationship

Programming language categories


27

Logic programming languages became the third major category

Advent of WEB drove the fourth Categories

Imperative C, Java, Perl, JavaScript, Visual BASIC

.NET, C++ Functional

LISP, Scheme, ML Logic

Prolog Markup/programming hybrid

JSTL, XSLT

Course


28

Practice at several exemplary programming languages

Focus more on C/C++ than the rest Learn the vernacular of formally

describing languages Gain some insight into how compilers

work

What should you study in this chapter?


29

Terminology Readability/ writability/ reliability (e.g. if a

language allows aliasing how does that affect reliability)?

Homework will give you some examples•Expression•Orthogonal•Syntax•Abstraction•Expressive•Aliasing

•Construct •Identifier

•Control structures•Compile

•Imperative•Functional

•Logic•JIT

•Interpreted•Hybrid

Programming Languages: lecture two

04/19/2330

Construct

04/19/23Introduction31

From construction, to construct something from smaller parts

(Wikipedia) A language construct is a syntactically allowable part of a program that may be formed from one or more lexical tokens in accordance with the rules of a programming language. Variable If/else Method/function/procedure Class

Return

Lexical


32

A lexicon is a dictionary Merriam-Webster

Main Entry: lex·i·cal Pronunciation: \ˈlek-si-kəl\Function: adjective Date: 18361 : of or relating to words or the vocabulary of a language

as distinguished from its grammar and construction2 : of or relating to a lexicon or to lexicography

Return

Orthogonality


33

Merriam-WebsterMain Entry: or·thog·o·nal

Pronunciation: \or-ˈthä-gə-nəl\Function: adjective Etymology: Middle French, from Latin orthogonius, from Greek

orthogōnios, from orth- + gōnia angle — more at -gonDate: 16121 a : intersecting or lying at right angles b : having perpendicular

slopes or tangents at the point of intersection <orthogonal curves>2 : having a sum of products or an integral that is zero or sometimes one under specified conditions: as a of real-valued functions : having the integral of the product of each pair of functions over a specific interval equal to zero b of vectors : having the scalar product equal to zero c of a square matrix : having the sum of products of corresponding elements in any two rows or any two columns equal to one if the rows or columns are the same and equal to zero otherwise : having a transpose with which the product equals the identity matrix 3 of a linear transformation : having a matrix that is orthogonal : preserving length and distance4 : composed of mutually orthogonal elements <an orthogonal basis of a vector space>5 : statistically independent

Return

Orthogonality (continued)


34

A relatively small set of primitive constructs can be combined in a relatively small number of ways

Every possible combination is legal, independent of context

Negative examples C:

Cannot return an array from a function Member of a struct can be any data type except void Members of an array can be any data type except void

Syntax

04/19/23Introduction35

Merriam-WebsterMain Entry: syn·tax

Pronunciation: \ˈsin-ˌtaks\Function: noun Etymology: Middle French or Late Latin; Middle French

sintaxe, from Late Latin syntaxis, from Greek, from syntassein to arrange together, from syn- + tassein to arrange

Date: 15741 a : the way in which linguistic elements (as words) are

put together to form constituents (as phrases or clauses) b : the part of grammar dealing with this2 : a connected or orderly system : harmonious arrangement of parts or elements <the syntax of classical architecture>3 : syntactics especially as dealing with the formal properties of languages or calculi

Expression


36

(Wikipedia) An expression is a combination of values, variables, operators, and functions that are interpreted (evaluated) according to the particular rules of precedence and of association for a particular programming language, which computes and then produces (returns, in a stateful environment) another value.

Examples: a a+b f(x) a==b

Return

Abstraction


37

(Wikipedia) Abstraction is the process or result of generalization by reducing the information content of a concept or an observable phenomenon, typically to retain only information which is relevant for a particular purpose. For example, abstracting a leather soccer ball to a ball retains only the information on general ball attributes and behavior. Similarly, abstracting happiness to an emotional state reduces the amount of information conveyed about the emotional state. Computer scientists use abstraction to understand and solve problems and communicate their solutions with the computer in some particular computer language.

Examples: Float is an abstraction for a real number An Employee object in a program is an abstraction for an

employee: doesn’t describe everything about an objectReturn

Recursion


38

Recursion is a method where the solution to a problem depends on solutions to smaller instances of the same problem.

Graham, Ronald; Donald Knuth, Oren Patashnik (1990). Concrete Mathematics. Chapter 1: Recurrent Problems. http://www-cs-faculty.stanford.edu/~knuth/gkp.html.

Donald Knuth wrote “The art of programming,” "father" of the analysis of algorithms, big O notation

The power of recursion evidently lies in the possibility of defining an infinite set of objects by a finite statement. In the same manner, an infinite number of computations can be described by a finite recursive program, even if this program contains no explicit repetitions.

Wirth, Niklaus (1976). Algorithms + Data Structures = Programs. Prentice-Hall. p. 126.

Niklaus Wirth wrote Pascal programming language

Recursion (continued)


39

Example Factorial

if x==1 then f(x)=1else f(x) = x * f(x-1)

Fibonacci By definition, the first two Fibonacci numbers are 0 and 1,

and each remaining number is the sum of the previous two. Some sources omit the initial 0, instead beginning the sequence with two 1s.

0 1 1 2 3 5 8 13 21 34 55 89 144 In mathematical terms, the sequence Fn of Fibonacci

numbers is defined by the recurrence relation F0=0 and F1 = 1 otherwise Fn=Fn-1+Fn-2 if x==0 then f(x)=0else if x==1 then f(x)=1else f(x) = x * f(x-1)

Recursion (continued)


40

Definition of the set of natural numbers 1 is in N If an element n is in N then n+1 is in N

Why no recursion early on


Efficient implementation of recursion generally requires a memory data structure known as a stack, and most computer architectures designed since the 1970s provide fast hardware support for stacks. The routine calling convention on the machines of the 1950s for which Fortran was originally developed stored the return address in the called routine, completely preventing recursion.

04/19/2341

Stack: local variables

Heap: dynamic allocation

Data: global variables

Text: program code

Reasons for Studying Programming Languages


Increased ability to express ideas

Improved background for choosing appropriate languages

Increased ability to learn new languages

Better understanding of significance of implementation

Better use of languages that are already known

Overall advancement of computing

04/19/2342

Where programming is used(Programming Domains)


43

Scientific applications Large numbers of floating point computations; use of

arrays Fortran

Business applications Produce reports, use decimal numbers and characters COBOL

Artificial intelligence Symbols rather than numbers manipulated; use of

linked lists LISP

Systems programming (operating system and supporting tools) Need efficiency because of continuous use C

Web Software Eclectic collection of languages: markup (e.g., XHTML),

scripting (e.g., PHP), general-purpose (e.g., Java)

Return

chapter one: metrics and influences on language design lesson 02

Documents

programming languages

target programming domain

expressions apl

excellent writability

particular programming

lecture two2 slide

reliability example

poor readability reliable