compilers-hw2

How to compile and run

make        
java [MainClassName] [file1] [file2] ... [fileN]

Architecture

4 components run in sequence:

1. SymTableVisitor → builds symbol table + duplicate checks
2. TypeCheckingVisitor → type checking using symbol table
3. OverridingOverloadingVisitor → method overloading/overriding rules
4. OffsetCalculator → calculates and prints field/method offsets

Visitor 1 - SymTableVisitor

1. Creates symbol table and checks for duplicate declaratioins
   

Symbol table structure:

• ClassName(String), ClassInfo:
  • Parent Name (String)
  • Variables: LinkedHashMap<String, String> — name -> type (order preserved)
  • Methods: LinkedHashMap<String, List> — name -> list of methods
    • MethodInfo:
      • Method Name (String)
      • Method Type/return type (String)
      • Formal Parameters: LinkedHashMap<String, String> — name -> type (order matters!)
      • Variables: LinkedHashMap<String, String> — name -> type

Checks:

• Duplicate class names
• Duplicate field names(int the same class)
• Duplicate local var name(in the same method)
• Duplicate parameter names(in the same method)
• Local variable cannot have same name as parameter

Helper Methods:

• MethodInfo getCurrentMethod(String className, String methodName) - returns the last added method — during Visitor 1 traversal the current method is always the last one added to the list

Design choices

• Methods stored as List per name to support overloading
• LinkedHashMap used everywhere to preserve insertion order
• Main class stored in symbol table with a MethodInfo for main to support type checking inside main body

Visitor 2 - TypeCheckingVisitor

Takes the symbol table from Visitor1 and performs type checking

1. Checks:

• Parent class exists
• Circular dependency
• Type validity checks(vars,methods,parameters, return types)
• Type checking in assignments
• Type checking in methods
• Array operations
• If/while conditions
• Print statements
• Return type

Helper Functions:

• checkType(var1, var2) — checks if var1 is subtype of var2
• checkMethod(classname, methodname) — finds method list in class or parents
• MethodInfo getCurrentMethod(String className, String methodName) - returns the last added method — during Visitor 1 traversal the current method is always the last one added to the list

Design Coices

• The visit(Identifier) function in visitor2 does not return the identifier name, instead it returns the type of the identifier. So in order to get identifier name i use i.fn.f0.toString() .
• If argu.methodName is null (class level context), returns the name string
• Always pass argu when visiting expressions — needed for variable lookup context
• argu.argTypes list collects method call argument types in MessageSend

Visitor 3 — OverridingOverloadingVisitor

Takes the symbol table and checks method overloading and overriding rules.
Rules are written in comments in the code

Helper Functions:

• checkType(var1, var2) — checks if var1 is same type or subtype of var2
• checkOverloading(classname) — checks overloading rules within the same class
• checkExtendBoth(classname, parentname) — checks overloading/overriding rules against parent chain

Design choices:

• checkExtendBoth walks up the inheritance chain recursively
• Two boolean flags used:
  • sameType — tracks if all argument positions have exactly the same types (override)
  • noSubtype — tracks if at least one position has no subtype relationship (valid overloading )

OffsetCalculator

Calculates and prints field/method offsets for each class.

Design choices:

• Uses LinkedHashMap for offsets to preserve declaration order
• Tracks total field/method size per class so subclasses know where to start
• Overridden methods don't get a new offset slot — they reuse the parent's slot
• Main class is skipped — it has no fields and main is static with no offset
• If parent is main class, child starts at offset 0

Helper Classes

• ClassInfo — holds class information (parent, fields, methods)
• MethodInf — holds method information (name, return type, params, locals)
• Argu — context passed through visitors (className, methodName, argTypes list)

Error handling

All errors reported via RuntimeException — program stops at first error per file but continues to next file.