Table-Driven Scanners

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2.13 Table-Driven Scanners

state = q0
IF( char undefined ){ char = nextChar(); }
WHILE( char != EOF ){
  IF( state == q0 ){
     str = "";
     IF( char == ’ ’ || char == ’\n’ ){
        char = nextChar();
        CONTINUE;
  }  }
  nextState = table[state, charMap[char] ];
  IF( nextState defined ){
     str += char;
     state = nextState;
     char = nextChar();
  }
  ELSE break;
}
IF( ! final(state) ){ error(); }

|------/------|
<blank > |-||| ||
|-| A–Z| ||-A–Z, |
- |-q0o --- | q1oo ||||0–9 ||
| 0–9| ||- ||
|-----| q2oo |||0–9 ||
| (,)| | ||
|-----| q3oo ||
| +,-| ||
|-----| q4oo |
| |
|--*--| q5oo else|- |
| / --||*||| | |||
------| q6oo --*||-q7o ||||||q8o ||-*
else |-

IF( state ==  q1 ){
  i = lookid(str)
  IF( i < 4 ) return(i,)
  ELSE        return(8,i)
}

symbol table


0	LET

1	GOTO

2	IF

3	END

	$⋮$ id $⋮$

IF( state ==  q2 ){
  value = parseInt(str)
  i = lookint( value )
  return(9,i)
}

constant table


0 1 $⋮$	$⋮$ int $⋮$

Note: lookid and lookint introduce the given arguments into the tables, if the values are not yet included in the tables

transition table


	0 A – Z	1 0 – 9	2 (,)	3 +,-	4 *	5 /

$q_{0}$	$q_{1}$	$q_{2}$	$q_{3}$	$q_{4}$	$q_{5}$	$q_{6}$

$q_{1}$	$q_{1}$	$q_{1}$

$q_{2}$		$q_{2}$

$q_{3}$

$q_{4}$

$q_{5}$

$q_{6}$					$q_{7}$

$q_{7}$	$q_{7}$	$q_{7}$	$q_{7}$	$q_{7}$	$q_{8}$	$q_{7}$

$q_{8}$	$q_{7}$	$q_{7}$	$q_{7}$	$q_{7}$	$q_{8}$	$q_{0}$

charMap


A	…	Z	0	…	9	(	)	+	-	*	/

0	…	0	1	…	1	2	2	3	3	4	5