Wu Hang
Introduction Requirements Checking Environment How to start Tips
Purpose ◦ Is syntactic analysis sufficient for program checking? ◦ What’s the differences between syntax and semantics? Approach ◦ After syntactic analysis What is a program?
See wiki ◦ Refer to gcc for any semantic issues not mentioned. ◦ Discuss when you find sth. strange. ◦ May test many cases ◦ Take everything into consideration
Type checking Use before declaration Duplicate variables Subscript checking Pointer checking (return value, parameters, assignment, etc.) Mismatch parameters of function or fields of record Break/continue out of a loop Struct checking (return value, parameters, assignment, etc.) Etc.
Mapping from a symbol to an entry Keep all information about variables, functions and types. VarEntry, FuncEntry, TypeEntry in one env Table.java
An entry keeps information about specific variable/function/type Must exists in some environment
+-*/ Lvalue Return value Make sure you have filled expr.type after checking
Top down/bottom up Deep understanding about the “program” you get after syntactic analysis Keep in mind what you NEED to do ◦ Try to write a program and run by gcc when you’re not sure whether it’s right or wrong.
Semantic semantic = new Semantic(program); for (int i = 0; i <program.declarationlist.size(); i++) { ◦ checkDeclarationlist(program.declarationlist[i]); }
void checkStmt(Stmt stmt) { if (stmt instanceof Ifstmt) checkIfstmt(stmt); … } Funtion Overloading
Get a variable to record loop ◦ Loop=0 When enter a loop ◦ Loop++; When leave a loop ◦ Loop--; When there is a continue/break ◦ If (loop>0) …
abstract class Type {} final class Void extends Type {} final class Char extends Type {} final class Int extends Type {} class Pointer extends Type { Type elementType; } final class Array extends Pointer { int capacity; }
final class Name extends Type { String name; } IT IS USED WHEN YOU SEE THIS: Struct node{ Int data; Struct node *next; };
abstract class Record extends Type { class RecordField { Type type; String name; } List fields; } final class Struct extends Record {} final class Union extends Record {} final class Function extends Type { Type argumentType; Type returnType; }
Boolean IsEqual(Type a, Type b) { If… }
What is the node’s class? ◦ instanceof Specify type ◦ getInstance() and equals(); static factory Return specific string ◦ Intern() Put attributes (lvalue, type, etc.) into the base class ◦ Simplify your code Copy a HashMap ◦ clone()
public class Symbol { private String name; private Symbol(String n) { name = n; } public String toString() { return name; } private static java.util.Dictionary dict = new java.util.Hashtable (); public static Symbol symbol(String n) { String u = n.intern(); Symbol s = dict.get(u); if (s == null) { s = new Symbol(u); dict.put(u, s); } return s; }
Q & A?
Thanks!