COMPILER ALGORITHM NOTATION: AN INTERPRETER AND COMPILER CS499 - B. Tech. Project

1. COMPILER ALGORITHM NOTATION: AN INTERPRETER AND COMPILER CS499 - B. Tech. Project Project Guide: Prof. S. K. Aggarwal Project Partners: Abhinav Bhatele (Y1008) Shubham Satyarth (Y1344)

2. THE PROBLEM We can divide the problem into five basic parts: Defining a language for writing compiler algorithms Writing an interpreter for the language Building a compiler to convert an algorithm to C code Providing a debugger Providing a GUI and web-enabled interface

3. MOTIVATION Development of new and faster algorithms for different parts of the compiler is a growing trend Algorithms generally written in pseudo-code Optimization is the heart of advanced compiler design This includes control and data flow analysis of programs These algorithms are generally written in complex notations We wish to save the compiler writer the trouble of writing algorithms in languages like C.

4. EXAMPLE 01 G: set of Productions procedure closure(I) returns set of Items I: in set of Items begin J: set of Items X: Items Y: Production J := I for each X INSET J do for each Y INSET G do if .Y NOTINSET J then J := J + .Y fi od od return J end

5. C code for Example 01 struct Items { // code for Items Items *next; } struct Production { // code for Production Production *next; } struct setofItems { Items head; } struct setofProductions { Production head }*G // Initialize G

6. C code for Example 01(contd.) void setofItems closure(setofItems I) { setofItems *J = I; setofProductions *K; K = G; Items *X; Items *X1; Production *Y; X = J->head; Y = G->head; while(X!=NULL) while(Y!=NULL) { Productions Z = K->head; while(K!=NULL) if(.Y==Z) { X1 = Z; X1->next = J->head; J->head = X1; } Z = Z->next; Y = Y->next; } X = X->next; return J; }

7. EXAMPLE 02 procedure exam(x, y) returns boolean x, y: out integer begin is: in intset INPUT is tv := true: boolean z: integer for each z INSET is (z > 0) do if x = z then return tv fi od return y INSET is end

8. C code for Example 02 boolean exam(int x, int y) { int n; printf("Enter the size of the set"); scanf("\%d",n); int is[n]; printf("Enter the set"); for(int i=0;i<n;i++) scanf("\%d",is[i]); boolean tv = true; for(int i=0;i<n;i++) if(is[i]==x) return tv; for(int i=0;i<n;i++) if(is[i]==y) return true; return false; }

9. CAL - The Language On the lines of Informal Compiler Algorithm Language (ICAN), we have defined a new language called Compiler Algorithm Language (CAL) It�s constructs are similar to languages like C and Pascal Allows using natural objects like sets and arrays Algorithms in compiler design can be easily converted into this form with minor modifications

10. CAL � Data Types and Operators Data Types Generic Simple Types: boolean, integer, real, character Constructed Types: enum, array � of, set of Compiler-specific Types: for example, Block = array [..] of array [..] of MIRInst Operators For Simple Types: +, -, *, /, %, ~,&,|,! For sets: UNION, INTERSECTION, INSET, NOTINSET,@, . , ?, SEQCONCAT, ELOFSEQ Conditional Operators: =, ?, <, =,>, =

11. CAL - Statements Simple Statements: Assignment Procedure call Return and Goto Input and Output Compound Statements: Beginning Internal Ending if elif, else fi case of, default esac for do od while do od repeat until

12. CAL - Keywords array begin boolean by case character default do each elif else end esac false fi for goto if in inout integer nil od of out procedure real repeat Return returns set to true until where while Additional Keywords: DIFF EXISTS FORALL NOTINSET NULL INSET OUTPUT UNION INPUT INTERSECTION

13. CAL � Program Structure A typical CAL file consists of: <type_definitions> <variable_declarations> <procedure_declarations> <optional_main_program> Type definitions: Type name followed by an equals sign and type expression Variable declaration: name of the variable followed by an optional initialization, followed by a colon and the variable�s type

14. CAL � Program Structure (contd.) Procedure declaration: Procedure�s name followed by its parameter�s list in parenthesis, an optional return type, followed by its parameter declarations and its body Main program: Has a form similar to other procedure

15. INTERPRETER � Implementation Front end of the interpreter: Lexical Analyzer (lexer.java): 33 types of tokens Syntax Analyzer (parser.java): more than 200 productions The back end or the executor consists of the following parts: Symbol Table cum Scratch Memory (SymbolTable.java) Virtual Machine (VirtualMachine.java) The Interpreter (MainProg.java)

16. Implementation Details One Pass Interpreter We do syntax directed evaluation Concept is similar to a Virtual Machine that does evaluation of statements and simulates a processor The Symbol Table is used as a memory also and is used by the virtual machine For procedure calls and loops, the virtual machine uses different objects of the executor

17. Implementation Details Each global variable encountered is directly stored in the symbol table Each procedure has an entry in the symbol table with a pointer to a file which stored the actual code This is done to avoid a second pass on the procedures Symbol Table for the procedure is initialized as soon as the procedure is encountered When there is a procedure call in main(), the code for that procedure is again parsed and this time executed

18. Symbol Table - Details A global symbol table with entries of global variables and procedures Each procedure including main has its own symbol table Two levels of the symbol table Outer level entries just have the lexeme and a pointer to the location where the actual value is stored Different linked lists for different data types like ArrList, SetList, etc. Each entry in the symbol table points to a particular entry in one of these linked lists

19. Symbol Table - Structure