A New CC Course – Based on Cooperation with Linz Vladimir Kurbalija, Mirjana Ivanović Department of Mathematics and Informatics University of Novi Sad Serbia and Montenegro

V. Kurbalija, M. Ivanović A New CC Course - Based on Cooperation with Linz Agenda Current CC Course in Novi Sad Current CC Course in Novi Sad Lectures Lectures Exercises Exercises CC Course in Linz CC Course in Linz Lectures Lectures Exercises Exercises Conclusion Conclusion

V. Kurbalija, M. Ivanović A New CC Course - Based on Cooperation with Linz CC Course in Novi Sad One of core software courses at Computer Science directions One of core software courses at Computer Science directions 7th semester CC1 (obligatory), 8th semester CC2 (elective), for students of 7th semester CC1 (obligatory), 8th semester CC2 (elective), for students of Computer Science, Computer Science, Business Computer Science, Business Computer Science, Teaching of Computer Science Teaching of Computer Science

V. Kurbalija, M. Ivanović A New CC Course - Based on Cooperation with Linz CC Course in Novi Sad - Lectures Practical approach Practical approach Development of Pascal- compiler Development of Pascal- compiler Subset of Pascal language: Subset of Pascal language: data types: Boolean and integer standard types, arrays and fixed records as structured types; data types: Boolean and integer standard types, arrays and fixed records as structured types; basic statements: assignment statement, procedure call, if and while statements; basic statements: assignment statement, procedure call, if and while statements; Standard input/output (read and write) procedures, user defined procedures including recursion. Standard input/output (read and write) procedures, user defined procedures including recursion.

V. Kurbalija, M. Ivanović A New CC Course - Based on Cooperation with Linz CC Course in Novi Sad - Lectures The implementation: The implementation: recursive-descent manner for syntax analysis recursive-descent manner for syntax analysis code generation for abstract P machine code generation for abstract P machine This approach was interesting 10 years ago This approach was interesting 10 years ago Now, when new languages and tools are appeared we need modernisation!!! Now, when new languages and tools are appeared we need modernisation!!!

V. Kurbalija, M. Ivanović A New CC Course - Based on Cooperation with Linz CC Course in Novi Sad - Exercises Students repeat and train practical skils gained during lectures Students repeat and train practical skils gained during lectures Several independent tasks – small grammars Several independent tasks – small grammars Implementation language is Modula-2 Implementation language is Modula-2 Compiler generator Coco/R Compiler generator Coco/R

V. Kurbalija, M. Ivanović A New CC Course - Based on Cooperation with Linz CC Course in Novi Sad - Exercises Tasks: Tasks: Lexical and syntax analysis and some parts of semantic analysis using Coco/R Lexical and syntax analysis and some parts of semantic analysis using Coco/R “Hand written” parsers (LA & SA) “Hand written” parsers (LA & SA) “Hand written” parsers with semantic analysis and rarely with code generation or interpretation “Hand written” parsers with semantic analysis and rarely with code generation or interpretation Some algorithms on grammars (memory organisation, checking consistency, computing first and follow sets…) Some algorithms on grammars (memory organisation, checking consistency, computing first and follow sets…)

V. Kurbalija, M. Ivanović A New CC Course - Based on Cooperation with Linz Agenda Current CC Course in Novi Sad Current CC Course in Novi Sad Lectures Lectures Exercises Exercises CC Course in Linz CC Course in Linz Lectures Lectures Exercises Exercises Conclusion Conclusion

V. Kurbalija, M. Ivanović A New CC Course - Based on Cooperation with Linz CC Course in Linz - Lectures One semester course held in English One semester course held in English The same course – at University of Oxford The same course – at University of Oxford Goals of the course Goals of the course acquire the practical skills to write a simple compiler for an imperative programming language acquire the practical skills to write a simple compiler for an imperative programming language understand the concepts of scanning, parsing, name management in nested scopes, and code generation. understand the concepts of scanning, parsing, name management in nested scopes, and code generation. learn to transfer the skills also to general software engineering tasks learn to transfer the skills also to general software engineering tasks

V. Kurbalija, M. Ivanović A New CC Course - Based on Cooperation with Linz CC Course in Linz - Lectures More theoretical approach More theoretical approach Course goes through all phases of a compiler writing Course goes through all phases of a compiler writing Shows the theoretical concepts underlying each phase as well as how to implement it efficiently Shows the theoretical concepts underlying each phase as well as how to implement it efficiently Examples: MicroJava compiler in Java, target language – subset of Java byte code Examples: MicroJava compiler in Java, target language – subset of Java byte code Example (05.SymbolTable.ppt, sl ) Example (05.SymbolTable.ppt, sl )

5.Symbol Table 5.1Overview 5.2Objects 5.3Scopes 5.4Types 5.5Universe

V. Kurbalija, M. IvanovićA New CC Course - Based on Cooperation with Linz Types Every object has a type with the following properties size (in MicroJava always 4 bytes) structure (fields for classes, element type for arrays,...) Kinds of types in MicroJava? primitive types ( int, char ) arrays classes Types are represented by structure nodes class Struct { static final int// type kinds None = 0, Int = 1, Char = 2, Arr = 3, Class = 4; int kind;// None, Int, Char, Arr, Class StructelemType;// Arr: element type intnFields;// Class: number of fields Objfields;// Class: list of fields }

V. Kurbalija, M. IvanovićA New CC Course - Based on Cooperation with Linz Structure Nodes for Primitive Types int a, b; char c; kind name type next val adr level nPars locals Var "a" Var "b" Var "c" kind elemType nFields fields Int - Char - object node structure node There is just one structure node for int in the whole symbol table. It is referenced by all objects of type int. The same is true for structure nodes of type char.

V. Kurbalija, M. IvanovićA New CC Course - Based on Cooperation with Linz Structure Nodes for Arrays int[] a; int b; kind name type next val adr level nPars locals Var "a" Var "b" kind elemType nFields fields Arr - The length of an array is statically unknown. It is stored in the array at run time. Int -

V. Kurbalija, M. IvanovićA New CC Course - Based on Cooperation with Linz Structure Nodes for Classes class C { int x; int y; int z; } C v; kind name type next val adr level nPars locals Type "C" - Var "v" kind elemType nFields fields Class - 3 Int - kind name type next val adr level nPars locals Var "x" Var "y" Var "z" - 2 -

V. Kurbalija, M. IvanovićA New CC Course - Based on Cooperation with Linz Type Compatibility: Name Equivalence Two types are the same if they are represented by the same type node (i.e. if they are denoted by the same type name) class T {...} T a; T b; Type "T"... Var "a"... Var "b"... Class -... The types of a and b are the same Name equivalence is used in Java, C/C++/C#, Pascal,..., MicroJava Exception In Java (and MicroJava) two array types are the same if they have the same element types!

V. Kurbalija, M. IvanovićA New CC Course - Based on Cooperation with Linz Type Compatibility: Structural Equivalence Two types are the same if they have the same structure (i.e. the same fields of the same types, the same element type,...) class T1 { int a, b; } class T2 { int c, d; } T1 x; T2 y; Type "T1"... Var "x"... Class - 2 The types of x and y are the same (but not in MicroJava!) Structural equivalence is used in Modula-3 but not in MicroJava and in most other languages! Var "a"... Var "b"... Type "T2"... Var "y"... Class - 2 Var "c"... Var "d"... Int -

V. Kurbalija, M. IvanovićA New CC Course - Based on Cooperation with Linz Methods for Checking Type Compatibility class Struct {... // checks if two types are compatible (e.g. in compare operations) public boolean compatibleWith (Struct other) { return (this.equals(other) ||this == Tab.nullType && other.isRefType() ||other == Tab.nullType && this.isRefType()); } // checks if "this" is assignable to "other" public boolean assignableTo (Struct other) { return (this.equals(other) ||this == Tab.nullType && other.isRefType()); } // checks if two types are the same (structural equivalence for arrays, name equivalence otherwise) public boolean equals (Struct other) { if (kind == Arr) return (other.kind == Arr && (other.elemType == elemType || other.elemType == Tab.noType)); else return (other == this); } public boolean isRefType() { return kind == Class || kind = Arr; } necessary because of standard function len(arr)

V. Kurbalija, M. IvanovićA New CC Course - Based on Cooperation with Linz Solving LL(1) Conflicts with the Symbol Table Method syntax in MicroJava void foo() int a; { a = 0;... } Actually we would like to write it like this void foo() { int a; a = 0;... } But this would result in an LL(1) conflict Block ="{" { VarDecl | Statement } "}". VarDecl =Type ident {"," ident}. Type =ident ["[" "]"]. Statement=Designator "=" Expr ";" |.... Designator=ident {"." ident | "[" Expr "]"}. First(VarDecl)  First(Statement) = {ident}

V. Kurbalija, M. IvanovićA New CC Course - Based on Cooperation with Linz Solving the Conflict With Semantic Information private static void Block() { check(lbrace); for (;;) { if (NextTokenIsType()) VarDecl(); else if (sym  First(Statement)) Statement(); else if (sym  {rbrace, eof}) break; else { error("...");... recover... } check(rbrace); } private static boolean NextTokenIsType() { if (sym != ident) return false; Obj obj = Tab.find(la.str); return obj.kind == Obj.Type; } Block = "{" { VarDecl | Statement } "}".

V. Kurbalija, M. Ivanović A New CC Course - Based on Cooperation with Linz CC Course in Linz – Exercises Students should acquire practical skills in compiler writing Students should acquire practical skills in compiler writing One (big) project divided in smaller subtasks One (big) project divided in smaller subtasks Students should write a small compiler for a Java-like language - MicroJava Students should write a small compiler for a Java-like language - MicroJava The implementation language is also Java The implementation language is also Java

V. Kurbalija, M. Ivanović A New CC Course - Based on Cooperation with Linz CC Course in Linz – Exercises The project consists of three levels: The project consists of three levels: Level 1 – implementation of a scanner and a parser for the language MicroJava, error handling Level 1 – implementation of a scanner and a parser for the language MicroJava, error handling Level 2 - deals with symbol table handling and type checking Level 2 - deals with symbol table handling and type checking Level 3 - deals with code generation for the MicroJava Level 3 - deals with code generation for the MicroJava

V. Kurbalija, M. Ivanović A New CC Course - Based on Cooperation with Linz CC Course in Linz – Exercises Study material: Study material: Teaching material (slides) Teaching material (slides) Description of the project Description of the project Specification of MicroJava language (tokens, language grammar, semantic and context constraints) Specification of MicroJava language (tokens, language grammar, semantic and context constraints) Specification of MicroJava virtual machine (similar but simpler than Java VM) – Memory layout and Instruction set Specification of MicroJava virtual machine (similar but simpler than Java VM) – Memory layout and Instruction set Specification of object file format Specification of object file format

V. Kurbalija, M. Ivanović A New CC Course - Based on Cooperation with Linz CC Course in Linz – Exercises Sources Sources Frameworks of all classes needed for compiler Frameworks of all classes needed for compiler Complete implementation of MicroJava VM Complete implementation of MicroJava VM Samples of MicroJava programs (for testing) Samples of MicroJava programs (for testing) program P { void main() int i; { i = 0; while (i < 5) { print(i); i = i + 1; }

V. Kurbalija, M. Ivanović A New CC Course - Based on Cooperation with Linz program Eratos char[] sieve; int max;// maximum prime to be found int npp;// numbers per page { void put(int x) { if (npp == 10) {print(chr(13)); print(chr(10)); npp = 0;} if (npp == 10) {print(chr(13)); print(chr(10)); npp = 0;} print(x, 5); print(x, 5); npp++; npp++;} void found(int x) int i; int i;{ put(x); put(x); i = x; i = x; while (i <= max) {sieve[i] = 'o'; i = i + x;} while (i <= max) {sieve[i] = 'o'; i = i + x;}} void main() int i; int i;{ read(max); read(max); npp = 0; npp = 0; sieve = new char[max+1]; sieve = new char[max+1]; i = 0; i = 0; while (i <= max) {sieve[i] = 'x'; i++;} while (i <= max) {sieve[i] = 'x'; i++;} i = 2; i = 2; while (i <= max) { while (i <= max) {found(i); while(i <= max && sieve[i] == 'o') i++; }}}//test

V. Kurbalija, M. Ivanović A New CC Course - Based on Cooperation with Linz Agenda Current CC Course in Novi Sad Current CC Course in Novi Sad Lectures Lectures Exercises Exercises CC Course in Linz CC Course in Linz Lectures Lectures Exercises Exercises Conclusion Conclusion

V. Kurbalija, M. Ivanović A New CC Course - Based on Cooperation with Linz Conclusion Contents of both courses is similar Contents of both courses is similar Approach is slightly different. In new course: Approach is slightly different. In new course: Lectures are purely theoretical Lectures are purely theoretical Exercises are more practical Exercises are more practical A newer programming language (Java) is used instead of Modula-2 A newer programming language (Java) is used instead of Modula-2 A target language (for code generation) is a subset of Java byte code instead of P-code A target language (for code generation) is a subset of Java byte code instead of P-code

V. Kurbalija, M. Ivanović A New CC Course - Based on Cooperation with Linz Conclusion Advantages of new course: Advantages of new course: Concepts of compiler construction are shown on more formal way Concepts of compiler construction are shown on more formal way Modern and object-oriented language is used (Java and Java byte code) Modern and object-oriented language is used (Java and Java byte code) Students autonomously write (almost) whole compiler Students autonomously write (almost) whole compiler Disadvantages of new course Disadvantages of new course Defining several language extensions for each student – students like to corporate during task solution  Defining several language extensions for each student – students like to corporate during task solution 

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