The Cool Reference ManualContents1 Introduction 32 GettingStarted 33 Classes 43.1 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43.2 Inheritance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 Types 64.1 SELF TYPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64.2 Type Checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 Attributes 85.1 Void . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 Methods 87 Expressions 97.1 Constants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97.2 Identiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97.3 Assignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97.4 Dispatch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107.5 Conditionals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107.6 Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117.7 Blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117.8 Let. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117.9 Case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127.10New . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127.11Isvoid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127.12Arithmetic and Comparison Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Copyright c 1995-2000byAlexAiken. Allrightsreserved.18 BasicClasses 138.1 Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138.2 IO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138.3 Int . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148.4 String . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148.5 Bool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149 MainClass 1410 LexicalStructure 1410.1Integers, Identiers, and Special Notation . . . . . . . . . . . . . . . . . . . . . . . . . . . 1510.2Strings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1510.3Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1510.4Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1510.5White Space . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1511 CoolSyntax 1711.1Precedence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1712 TypeRules 1712.1Type Environments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1712.2Type Checking Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1813 OperationalSemantics 2213.1Environment and the Store . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2213.2Syntax for Cool Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2413.3Class denitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2413.4Operational Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2514 Acknowledgements 3021 IntroductionThis manual describes the programming language Cool: the Classroom Object-Oriented Language. Coolis a small language that can be implemented with reasonable eort in a one semester course. Still, Coolretainsmanyof thefeaturesof modernprogramminglanguagesincludingobjects, statictyping, andautomatic memory management.Cool programs are sets of classes. A class encapsulates the variables and procedures of a data type.Instances of a class are objects. In Cool, classes and types are identied; i.e., every class denes a type.Classes permit programmers to dene new types and associated procedures (or methods) specic to thosetypes. Inheritance allows new types to extend the behavior of existing types.Cool isanexpressionlanguage. MostCool constructsareexpressions, andeveryexpressionhasavalue and a type. Cool is type safe: procedures are guaranteed to be applied to data of the correct type.While static typing imposes a strong discipline on programming in Cool, it guarantees that no runtimetype errors can arise in the execution of Cool programs.This manual is divided into informal and formal components. For a short, informal overview, the rsthalf (through Section 9) suces. The formal description begins with Section 10.2 GettingStartedThereaderwhowantstogetasenseforCool attheoutsetshouldbeginbyreadingandrunningtheexampleprogramsinthedirectory~cs164/examples. Cool sourceleshaveextension.clandCoolassembly les have extension.s. The Cool compiler is~cs164/bin/coolc. To compile a program:coolc [ -o fileout ] file1.cl file2.cl ... filen.clThe compiler compiles the lesfile1.cl throughfilen.cl as if they were concatenated together.Eachlemustdeneasetofcompleteclassesclassdenitionsmaynotbesplitacrossles. The-ooption species an optional name to use for the output assembly code. Iffileout is not supplied,theoutput assembly is namedfile1.s.ThecoolccompilergeneratesMIPSassemblycode. Becausenotallofthemachinesthecourseisusing are MIPS-based, Cool programs are run on a MIPS simulator called spim. To run a cool program,type% spim(spim) load "file.s"(spim) runTo run a dierent program during the samespim session,it is necessary to reinitialize the state of thesimulator before loading the new assembly le:(spim) reinitAn alternativeand fasterway to invokespim is with a le:spim -file file.sThis form loads the le, runs the program, and exitsspim when the program terminates. Be sure thatspimisinvokedusingthescript~cs164/bin/spim. Theremaybeanotherversionofspiminstalledinon some systems, but it will not execute Cool programs. An easy way to be sure of getting the correct3version is to aliasspim to~cs164/bin/spim. Thespim manual is available on the course Web page andin the course reader.The following is a complete transcript of the compilation and execution of ~cs164/examples/list.cl.This program is very silly, but it does serve to illustrate many of the features of Cool.% coolc list.cl% spim -file list.sSPIM Version 5.6 of January 18, 1995Copyright 1990-1994 by James R. Larus (larus@cs.wisc.edu).All Rights Reserved.See the file README a full copyright notice.Loaded: /home/ee/cs164/lib/trap.handler5 4 3 2 14 3 2 13 2 12 11COOL program successfully executed%3 ClassesAll code in Cool is organized into classes. Each class denition must be contained in a single source le,but multiple classes may be dened in the same le. Class denitions have the form:class [ inherits ] {

};The notation [ ...]denotes an optional construct. All class names are globally visible. Class namesbegin with an uppercase letter. Classes may not be redened.3.1 FeaturesThe body of a class denition consists of a list of feature denitions. A feature is either an attribute oramethod. AnattributeofclassAspeciesavariablethatispartofthestateofobjectsofclassA. Amethod of classA is a procedure that may manipulate the variables and objects of classA.One of the major themes of modern programming languages is information hiding, which is the ideathatcertainaspectsofadatatypesimplementationshouldbeabstractandhiddenfromusersofthedata type. Cool supports information hiding through a simple mechanism: all attributes have scope localto the class, and all methods have global scope. Thus, the only way to provide access to object state inCool is through methods.Feature names must begin with a lowercase letter. No method name may be dened multiple times ina class, and no attribute name may be dened multiple times in a class, but a method and an attributemay have the same name.A fragment fromlist.cl illustrates simple cases of both attributes and methods:4class Cons inherits List {xcar : Int;xcdr : List;isNil() : Bool { false };init(hd : Int, tl : List) : Cons {{xcar