Compiler 2013: An appetizer

This page illustrates a complete process of a toy compiler as a tutorial. The source code is available at https://bitbucket.org/xjia/appetizer

Example 1

int main()
{
  int a;
  int b;
  int c;
  int max;

  a = 10;
  b = 10 * 3;
  c = 10 + 10;

  max = a;
  if (b > max) { max = b; }
  if (c > max) { max = c; }
  return max;
}

The result is 30.

Example 2

int main()
{
  int a;
  int b;

  a = 0;
  b = 10;

  {
    int b;
    b = 20;
    a = a + b;
  }

  return a;
}

The result is 20.

Example 3

int main()
{
  int a;
  a = 10;
  if (a > 0) return a;
  return 0;
}

The result is 10.

Grammar

The ANTLR grammar is given as follows.

grammar Appetizer;

program : 'int' ID '(' ')' block
        ;
block : '{' decl* stmt* '}'
      ;
decl : 'int' ID ';'
     ;
stmt : 'if' '(' expr ')' stmt
     | 'return' expr ';'
     | expr ';'
     | block
     ;
expr : expr ('*'|'/') expr
     | expr ('+'|'-') expr
     | expr ('=='|'!='|'>'|'>='|'<'|'<=') expr
     | expr '=' expr
     | ID
     | NUM
     | '(' expr ')'
     ;
ID : [a-z]+ ;
NUM : [0-9]+ ;
WS : [ \t\f\r\n]+ -> skip ;

Functions and arrays are not allowed. Comments are nested, and enclosed with /* and */.

In this tutorial, we use JFlex for lexing and CUP for parsing.