Mini C Compiler

Compilers can be decomposed into several phases, each of which converts one form of source program into another
There are different phases of compiler as follow:

• Lexical analysis (Implemented)
• Syntax analysis (Implemenetd)
• Semantic analysis
• Intermediate code generation
• Code optimization
• Code generation

Lexical analysis

Source program is scanned to read the stream of characters and those characters are grouped to form a sequence called lexemes which produces token as output.

• Token: Token is a sequence of characters that represent lexical unit, which matches with the pattern, such as keywords, operators, identifiers etc.
• Lexeme: Lexeme is instance of a token i.e., group of characters forming a token.
• Pattern: Pattern describes the rule that the lexemes of a token takes. It is the structure that must be matched by strings.
  ```
  …
  …
  SINGLE_COMMENT \/\/.+
  MULTI_COMMENT \/*(.|\n)?\\/ ?
  INTEGRAL_LITERAL \b0|[1-9][0-9]\b
  FlOAT_LITERAL [0-9]+.[0-9]+
  CHAT_LITERAL \’[a-zA-z0-9]\’
  STRING_LITERAL \”.\”
  …
  …

```

Syntax Analysis

Syntax analysis is the second phase of compiler which is also called as parsing.

• Parser converts the tokens produced by lexical analyzer into a tree like representation called parse tree.
• A parse tree describes the syntactic structure of the input.

Parser follow production rules (Grammer) defined by means of context free grammar (CFG).


Grammer ex:

program -> decl_list  
decl_list -> decl decl_list'  
decl_list' -> decl decl_list' | ϵ  
decl -> var_decl | fun_decl  
var_decl -> type_spec IDENT var_decl'  
var_decl' -> ; | [ ] ;  
type_spec -> VOID  
            | BOOL  
            | INT  
            | FLOAT
...
...
...

The way the production rules are implemented divides parsing into two types : top-down parsing and bottom-up parsing. I use Recursive descent parser is a kind of top-down parser.

Example

Input

int main(){  
    int x;  
}

Genereted Tokens from Lexical analyzer

<INT>: int  
<ID>: main  
<LEFT_ROUND_B>: (  
<RIGHT_ROUND_B>: )  
<LEFT_CURLY_B>: {  
<INT>: int  
<ID>: x  
<SEMICOLON>: ;  
<RIGHT_CURLY_B>: }

Genereted Parse Tree from Syntax Analyzer