Course Project - Compiler Construction - Lecture Slides, Slides of Compiler Construction

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Lecture Outline

• Cool

• The Course Project

• Programming Assignment 1

Cool Overview

• Classroom Object Oriented Language

• Designed to

• Be implementable in one semester
• Give a taste of implementation of modern
  • Abstraction
  • Static typing
  • Reuse (inheritance)
  • Memory management
  • And more …

• But many things are left out

Cool Objects

• An object can be thought of as a record

with a slot for each attribute

class Point { x : Int  0; y : Int; ( use default value ) };

x y

• The expression “new Point” creates a new

object of class Point

Methods

• Methods can refer to the current object using self

class Point { x : Int  0; y : Int  0; movePoint(newx : Int, newy : Int): Point { { x  newx; y  newy; self; } -- close block expression }; -- close method }; -- close class

• A class can also define methods for manipulating the attributes

Methods

• Each object knows how to access the code of a method
• As if the object contains a slot pointing to the code
  • In reality implementations save space by sharing these pointers among instances of the same class

x y 0 0

movePoint

x y 0 0

methods movePoint

Inheritance

• We can extend points to colored points using

subclassing => class hierarchy

class ColorPoint inherits Point { color : Int  0; movePoint(newx : Int, newy : Int): Point { { color  0; x  newx; y  newy; self; } }; }; x y 0 0

color 0

movePoint

Cool Type Checking

• Is well typed if P is an ancestor of C in the

class hierarchy

• Anywhere an P is expected a C can be used

• Type safety:

• A well-typed program cannot result in runtime type errors

x : P; x  new C;

Method Invocation and Inheritance

• Methods are invoked by dispatch

• Understanding dispatch in the presence of

inheritance is a subtle aspect of OO languages

p : Point; p  new ColorPoint; p.movePoint(1,2);

 p has static type Point  p has dynamic type ColorPoint  p.movePoint must invoke the ColorPoint version

Other Expressions

• Expression language (every expression has a

type and a value)

• Conditionals if E then E else E fi
• Loops: while E loop E pool
• Case statement case E of x : Type  E; … esac
• Arithmetic, logical operations
• Assignment x  E
• Primitive I/O out_string(s), in_string(), …

• Missing features:

• Arrays, Floating point operations, Interfaces, Exceptions,…

Cool Memory Management

• Memory is allocated every time new is invoked

• Memory is deallocated automatically when an

object is not reachable anymore

• Done by the garbage collector (GC)
• There is a Cool GC

Programming Assignment I

• Write an interpreter for a stack machine …

• … in Cool

• Due in 2 weeks

• Must be completed individually

Homework for Next Week

• Work on Programming Assignment I

• Read Chapters 1-2 of Textbook

• Continue learning Flex/Jlex