1.5 KiB
Semantic Analysis
- after passing the lexical and syntax analysis, there are still errors. so correcting usage of variables, objects and function... are needed.
Semantic Analysis ensures the program satisfies a set of rules regarding the usage of programming constructs:
- identifiers declared before used
- types
- inheritance relationships
- single definition
Categories of Semantic Analysis
- Scopes
- Types
Scope
Lexical Scope: textual region in the program
Symbol Tables
Symantic checks refer to properties of identifier in the program; it need an environment to store identifier info: symbol table.
| name | kind | type |
|---|---|---|
| foo | func | int -> int |
| m | arg | int |
| n | arg | int |
| tmp | var | char |
Each scope has symbol tables. And program has hierachy of symbol tables(scope).
if the identifier is used traverse the hierachy of symbol tables upward until finding the identifier with the same name to determine the declaration from the current scope.
Build a Symbol Table
there are five operations:
- insert scope
- exit scope
- find symbol(x)
- add symbol(x)
- check scope(x)
Type
- Type checking
- Type inferencing
Three Language Types:
- Statically typed
- Dynamically typed
- Untyped(machine code)
Static Type Checking Does not require additional type checking instructions at runtime. and guarantees that the executions are safe at compile time. modern languages require both static and dynamic type checking(union, void ptr)