1. CS252 Lab 2 Prepared by El Kindi Rezig

2. Notes Check out new version of the “official” fiz interpreter at https://www.cs.purdue.edu/homes/ninghui/courses/252_Spri ng15/code/fizlab/fizhttps://www.cs.purdue.edu/homes/ninghui/courses/252_Spri ng15/code/fizlab/fiz New functionality: tracing

3. Use “help” in the interpreter fiz> help You can use the following commands: import tracing on tracing off (define ( >) >) > The grammar for > is: > ::= (inc >) | (dec >) | (ifz > > >) | (halt) | ( >)

4. Result of tracing (for add) fiz> tracing on fiz> (add 3 2) Evaluating (add 3 2) Evaluating (ifz 2 3 (add (inc..) (dec..))) Evaluating (add 4 1) Evaluating (ifz 1 4 (add (inc..) (dec..))) Evaluating (add 5 0) Evaluating (ifz 0 5 (add (inc..) (dec..))) (add 5 0) = 5 (add 4 1) = 5 (add 3 2) = 5 5

5. Result of tracing (for sub) fiz> (sub 3 2) Evaluating (sub 3 2) Evaluating (ifz 2 3 (ifz 3 (halt) (sub (dec..) (dec..)))) Evaluating (ifz 3 (halt) (sub (dec..) (dec..))) Evaluating (sub 2 1) Evaluating (ifz 1 2 (ifz 2 (halt) (sub (dec..) (dec..)))) Evaluating (ifz 2 (halt) (sub (dec..) (dec..))) Evaluating (sub 1 0) Evaluating (ifz 0 1 (ifz 1 (halt) (sub (dec..) (dec..)))) (sub 1 0) = 1 (sub 2 1) = 1 (sub 3 2) = 1 1

6. Notes Try write some fiz programs using the interpreter E.g., write (max x y z), which outputs the max value among x,y,z. Do it from the ground up Will help you in the exam

7. Formal and Actual Arguments Arguments are also known as parameters Formal arguments/parameters appear in function definition Actual arguments/parameters appear in function calls E.g., (define (add x y) (ifz y x (add (inc x) (dec y)))) (add 3 2) Formal Actual

8. Overview -Lab 2 has two parts: 1.FIZ without user-defined functions (50%): Parse and evaluate built-in FIZ functions. 2.Support of user-defined functions’ declarations and calls (50%): Parse and evaluate user-defined functions’ declarations and calls.

9. Lab 2: Part 1 (FIZ without user-defined functions) The language grammar: : (inc ) | (dec ) | (ifz ) | (halt) | NUMBER All expressions evaluate to a non-negative integer value.

10. Lab 2: Part 1 (FIZ without user-defined functions) Example statements that are supported by FIZ: (inc (inc 5)) // interpreter prints 6 (dec (inc (dec 3))) // interpreter prints 2 (dec (ifz 0 4 (inc 1))) // interpreter prints 3 Example statements that are NOT supported by FIZ: (inc 4 5) // Error: inc only takes 1 argument. (ifz 0 halt) // Error: halt used without parenthesis, no else statement (inc (dec )) //Error: no argument for “dec”.

11. Lab 2: Part 1 (FIZ without user-defined functions) TODO -Implement the scanner and parser. -For any newly added files, type: 1.git add {new file name} 2.git commit -am "description of the changes you have made." 3.git push -You need to push all your changes before: 02/09/2015, 11:59pm.

12. Lab 2: (support of user-defined functions’ declaration and calls) (50%) -Parse and evaluate user-defined functions’ declarations and calls. -Add to the parser to parse the following: 1.(define (ID +) ) 2.(ID +) -Evaluate the user-defined declarations and calls.

13. Lab 2: (support of user-defined functions’ declaration and calls) (50%) nameargNamesbody numArgs FUNC_DECL structure definition: foo 1 x Example: (define (foo x) (inc x)) INC FUNC_DECL TREE_NODE NODE TYPE name numArgsargNames body x ARG_NAME Could be a size-10 array, with only the first element used

14. Lab 2: (support of user-defined functions’ declaration and calls) (50%) add 2 xIFZ NODE TYPE Example: (define (add x y) (ifz y x (add (inc x) (dec y)))) y FUNC_CALL add2 argNames numArgs name numArgs body FUNC_DECL INC DEC y ARG_NAME x x y Could be a size-10 array, with only the first two elements used

15. Lab 2: (support of user-defined functions’ declaration and calls) (50%) add 2 args numArgs INC NUMBER_NODE 2 FUNC_CALL Example: (add (inc 1) 2) name 1.Resolve expression NUMBER_NODE 1

16. Lab 2: (support of user-defined functions’ declaration and calls) (50%) 2 args numArgs INC NUMBER_NODE 2 FUNC_EVAL Example: (add (inc 1) 2) func 1.Resolve expression add 2 xIFZyyx FUNC_CALLadd 2 FUNC_DECL INC DEC NUMBER_NOD E 1 Add reference to the function declaration structure x ARG_NAME y x y

17. Lab 2: (support of user-defined functions’ declaration and calls) (50%) 2 args numArgs INC NUMBER_NODE 2 FUNC_EVAL Example: (add (inc 1) 2) func 1.Resolve expression add 2 xIFZyyx FUNC_CALLadd 2 FUNC_DECL INC DEC NUMBER_NOD E 1 Add reference to the function declaration structure x ARG_NAME y x y 2. Evaluate parameters

18. Lab 2: (support of user-defined functions’ declaration and calls) (50%) 2 args numArgs INC NUMBER_NODE 2 FUNC_EVAL Example: (add (inc 1) 2) func 1.Resolve expression 2.Evaluate parameters eval() 2 add 2 xIFZyyx FUNC_CALLadd 2 FUNC_DECL INC DEC NUMBER_NOD E 1 x ARG_NAME y x y

19. Lab 2: (support of user-defined functions’ declaration and calls) (50%) 2 args numArgs NUMBER_NODE 2 FUNC_EVAL Example: (add (inc 1) 2) func 1.Resolve expression 2.Evaluate parameters eval() 2 2 INC add 2 xIFZyyx FUNC_CALLadd 2 FUNC_DECL INC DEC NUMBER_NOD E 1 x ARG_NAME y x y

20. Lab 2: (support of user-defined functions’ declaration and calls) (50%) add 2 xIFZyyx FUNC_EVAL 2 FUNC_DECL INC DEC NUMBER_NOD E 1 x ARG_NAME y x y 1.Resolve expression 2.Evaluate parameters 3.Resolve body of add

21. Lab 2: (support of user-defined functions’ declaration and calls) (50%) add 2 xIFZyyx FUNC_EVAL 2 FUNC_DECL INC DEC NUMBER_NOD E 1 x ARG_NAME y x y 1.Resolve expression 2.Evaluate parameters 3.Resolve body of add 4.Pass computed params to the function.

22. Lab 2: (support of user-defined functions’ declaration and calls) (50%) TODO for this part 1.Add the (define) construct into the grammar. 2.Function declaration: Build the AST for each user- defined function and store it. 3.Function call: Lookup the AST of the called function, and evaluate its branches using the provided parameters. 4. You need to push all your changes before: 02/16/2015, 11:59pm.

23. Where to Add Your Code in fiz.y? %token INC OPENPAR CLOSEPAR// more tokens %type expr // more non-terminals enum NODE_TYPE{ INC_NODE, NUMBER_NODE,// more node types }; struct TREE_NODE{ enum NODE_TYPE type; union { struct TREE_NODE *first_arg; int intValue; // more union members for other node types };

24. Union in C union { struct TREE_NODE *first_arg; int intValue; // more union members for other node types // such as struct { … } field; }; A union stores different data types in the same memory location In the union above, first_arg and intValue refer to the same memory location, as is any other additional member in the union. The size of a union is the max of the size of all its components. A union member can be a struct as well.

25. Why Use Union Reason 1: Want to access the same data in different ways, e.g., an IP address, or a hardware register can be defined as union { struct { unsigned char byte1; unsigned char byte2; unsigned char byte3; unsigned char byte4; } bytes; unsigned int word; } HW_Register; reg.dword = 0x12345678; reg.bytes.byte3 = 4; Similarly, using a union for an IP address allows access individual bytes in the address as well as treating them as integer

26. Why Use Union Reason 2: Implement pseudo-polymorphism. A structure may include different types of data (e.g., a TREE_NODE in FIZ interpreter may be of several different types). A field, type, indicates which type of node this is. The union includes the actual data needed for this type of node. Typically, assigning value to and retrieving from the node should use the same union member. See code for example.

27. Where to Add Your Code in fiz.y? struct FUNC_DECL { char *name; // Other information of the function needs to be added }; // More grammar rules statement: OPENPAR DEFINE OPENPAR … // define a function expr: … // handle function call // auxiliary rules that may be needed to define the above two

28. Where to Add Your Code in fiz.y? void resolve (struct TREE_NODE *node, struct FUNC_DECL *cf){ // cf==NULL when resolving an expression as a statement // cf points to the function when resolving a function // body switch(node->type) { // Add code to resolve appearances of function names, and // usage of arguments if we are resolving the body of a // function } return; }

29. Where to Add Your Code in fiz.y? int eval(struct TREE_NODE * node, int *env){ // env=NULL when evaluating an expression as a statement // env points to an array of actual arguments when evaluating the // body of a function switch(node->type){ case NUMBER_NODE: return node->intValue; case INC_NODE: return eval(node->first_arg, env) + 1; // Add code to evaluate other kinds of expressions, especially // a function call, for which we need to evaluate the actual // arguments first, and then evaluate the body, passing in the // array of actual argument values }

30. Avoiding Buffer Overflow and Memory Leak Count as 10% extra credit for Lab 2. Avoid buffer overflow: avoid using fixed-size buffer for identifiers Avoid memory leak: Free allocated memory when no longer needed An expression statement after evaluated Define statement when there is an error in functional definition Possibly other things