Systematic Development of Programming Languages

cs7100(Prasad) L1Intro 1

Systematic Development of Programming Languages


Orthogonal Parameters

Conceptual view (Model of Computation)» imperative, functional, relational,...

Level of abstraction (Model of Implementation)» problem domain

» ...

» machine

– Computational Task : I/O relation to be implemented


1. Customized Digital Computer

OjIj

Ik Ok

Task j

Task k

Rig different circuit for each task


von Neumann showed the existence of a Universal Machine (hardware) that can be customized using control inputs to carry out different tasks.

Software is the encoding of the task to control this machine.

2. Stored Program Computing

encoding(Tj)Ij Oj


Imperative Languages

Model of Computation» ALU + Memory + Input + Output

(von Neumann architecture) Levels of Abstraction (“Human Interface”)

– Machine Language » Binary Representation of the task

– Assembly Language» Symbolic Representation of the task

Assembly Language

Use symbols instead of binary digits to describe fields of instructions.

Every aspect of machine visible in program:– One statement per machine instruction.

– Register allocation, call stack, etc. must be managed explicitly.

No structure: everything looks the same.

10101100100000100000000000010101ADDI R4 R2 21

ADDI R4,R2,21



Pros and Cons of Assembly Language

Avoids Absolute Addressing» relocatable, reusable/shareable

Uses Symbolic Names» readable

Low-level programming wastes effort in coding a solution rather than solving a problem.

Difficult to build and maintain large programs.


High-level Language

Provides notation to describe problem solving strategies rather than organize data and instructions at machine-level.

Improves programmer productivity by supporting features to abstract/reuse code, and to improve reliability/robustness of programs.

Requires a compiler.


Levels of Abstraction

Problem Domain (stacks, tables)

Machine (char, int)

C++

(Class Hierarchies) Java/C#/Scala/Python/Scheme/Clojure

Ada

CPascal

Assembly Language

(ADTs) (arrays)


Evolution of Programming Languages

• FORTRAN ( FORmula TRANslator) Goals : Scientific Computations Efficiency of execution Compile-time storage determination Features : Symbolic Expressions Subprograms Absence of Recursion

• COBOL Goal: Business Application Features : Record/Structure; File Handling



• ALGOL - 60 (ALGOrithmic Language)

Goals : Communicating AlgorithmsFeatures : Block Structure (Top-down design) Recursion (Problem-solving strategy) BNF - Specification

• LISP (LISt Processing) Goals : Manipulating symbolic information Features : List Primitives Interpreters / Environment


Problems

Not rugged wrt typographical errorsDo 10 I = 1.20 I5 = I5 + 1

vs vs

Do 10 I = 1,20 I5 = IK + 1

– Remedy: Use spaces to delimit tokens,

Declare before use Unintended Coercion

I > J and false

– Remedy: Type checking



• Pascal Goal : Structured Programming, Type checking, Compiler writing. Features :

• Rich set of data types for efficient algorithm design

• E.g., Records, sets, ...• Variety of “readable” single-entry single-exit control structures

• E.g., for-loop, while-loop,...• Efficient Implementation

• Recursive descent parsing


Programming in the Large

Programs no longer monolithic. Developed by a team of programmers.

Code sharing and reuse very important. Correctness, reliability, and robustness

essential.– Data Abstraction / Encapsulation / Strong

Typing» Ada, CLU, Modula etc.


Other Languages Functional

» Common LISP, Scheme, Clojure» ML, Haskell

Logic » Prolog

Object-oriented» Smalltalk, SIMULA, Modula-3, Oberon» C++, Eiffel, Ada-95, Java, C#

Hybrid» Python, Ruby, Scala

Application specific languages and tools


Scripting vs Systems Programming Languages

Designed for gluing applications : flexibility

Interpreted Dynamic typing and

variable creation Data and code integrated :

meta-programming supported

Examples: PERL, Tcl, Python, Ruby, PHP, Scheme, Visual Basic, etc.

Designed for building applications : efficiency

Compiled Static typing and variable

declaration Data and code separated :

cannot create/run code on the fly

Examples: PL/1, Ada, Java, C, C++, C#, Scala, etc.


(cont’d)

Does application implement complex algorithms and data structures?

Does application process large data sets (>10,000 items)? Are application functions well-defined, fixed?If yes, consider a system programming language.

Is the main task to connect components, legacy apps? Does the application manipulate a variety of things? Does the application have a GUI? Are the application's functions evolving rapidly? Must the application be extensible? Does the application do a lot of string manipulation?If yes, consider a scripting language.


Jython (for convenient access to Java APIs)

I:\tkprasad\cs7100>jython

…

>>> import javax.swing as swing

>>> win = swing.JFrame("Welcome to Jython")

>>> win.size = (200, 200)

>>> win.show()

>>> ^Z


Java vs Jython

map = new HashMap();map.put("one",new Integer(1));map.put("two",new Integer(2));map.put("three",new Integer(3));

System.out.println(map.get("one"));

list = new LinkedList();list.add(new Integer(1));list.add(new Integer(2));list.add(new Integer(3));

map =

{"one":1,"two":2,"three":3}

print map ["one"]

list = [1, 2, 3]


(cont’d)

for i in list:

(* iterator *)

newList = [function(i) for i in oldList]

(* list comprehension *)

for (Iterator i; i.hasNext();) { i.next(); }

List newList = ArrayList()for (Iterator i; i.hasNext();) {

Object obj = i.next(); newList.add(function(obj))

}


Functional Programming in Jython

apply(lambda x,y : x*y, (10, 20))# 200map(lambda x,y: x + y, [[1,2],[“a”]], [[“3”],[“b”]])# [[1, 2, ‘3’], [‘a’, ‘b ’]]reduce(lambda x,y: x + y, [1,2,3], 100)# 106filter(lambda x: x > 0, range(10,-5,-3))# [10, 7 , 4, 1]


Meta-programming in Jython

Dynamic code evaluation

print eval (“[1,3] + range(6,10,3)”)

# [1, ,3, 6, 9]x = 2 + 3jexec “x = 5, x + x”#(5, (4+6j)


import java.lang as langimport javax.swing as swingimport java.awt as awt

names = ["Groucho", "Chico", "Harpo"]quotes = {"Groucho": "Say the secret word", "Chico": "Viaduct?",

"Harpo": "HONK!"}

def buttonPressed(event): field.text = quotes[event.source.text]

def exit(event): lang.System.exit(0) def createButton(name): return swing.JButton(name, preferredSize=(100,20),

actionPerformed=buttonPressed)

Java functionality through Jython


win = swing.JFrame("Welcome to Jython", size=(200, 200),windowClosing=exit)

win.contentPane.layout = awt.FlowLayout( )

field = swing.JTextField(preferredSize=(200,20))win.contentPane.add(field)

buttons = [createButton(each) for each in names]

for eachButton in buttons: win.contentPane.add(eachButton)

win.pack( )win.show( )

Current Trend Multiparadigm languages

– Functional constructs for programming in the small » Focus on conciseness and correctness

– Object-Oriented constructs for programming in the large

» Focus on programmer productivity, robustness and code evolution

Example languages

– Older: Python, Ruby

– Recent: Scala, F#



Scheme (dialect of LISP) Recursive definitions Symbolic computation : List Processing Higher-order functions Dynamic type checking Functional + Imperative features Automatic storage management

– Provides a uniform executable platform for studying, specifying, and comparing languages.


DrRacket (IDE for dialect of LISP)

http://docs.racket-lang.org/quick/

http://docs.racket-lang.org/teachpack/2htdp2htdp.html

http://picturingprograms.com/download/chap03.pdf









Standard ML and Scala

Strongly typed language– static type inference– SML supports polymorphic types

Supports Abstract Data Types and Modules Higher-order functions Pattern matching

– cf. Prolog, list-processing in Scheme

Java vs Scala//Java - what we're used to seeing

public String buildEpochKey(String... keys) {StringBuilder s = new StringBuilder("elem") for(String key:keys) { if(key != null) { s.append(".") s.append(key) } } return s.toString(). toLowerCase()}


Java vs Scala//Scala

def buildEpochKey(keys: String*): String = { ("elem" +: keys) . mkString(".") . toLowerCase}

println(buildEpochKey("aBcDeF"))


Systematic Development of Programming Languages

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