First lex script. Parsing C expressions.

Hello. I'm writing my first lex-fil. It's supposed to recognize tokens
from C - ultimately, I want to match expressions. An expression can
contain an expression - so there is recursion allowed.


My definitions section looks like this:


DATATYPES
union|enum|struct|char|double|float|long|short|signed|int|unsigned|void
STORAGE_CLASS volatile|register|auto|extern|static|const
RESERVED
break|case|continue|default|do|else|for|goto|if|return|sizeof|switch|typedef|while
KEYWORDS {DATATYPES}|{STORAGE_CLASS}|{RESERVED}
W [ \t]* /*
Whitespace */
DIGIT [0-9] /*
Digit */
INTEGER {DIGIT}+ /*
Integer constant */
HEXADECIMAL 0x{INTEGER}|0X{INTEGER} /*
Hexadecimal representation */
DECIMAL {DIGIT}*"."{INTEGER} /*
Float constant */
NUMBER {INTEGER}|{DECIMAL}|{HEXADECIMAL} /*
Numerical constant*/
IDENTIFIER [_a-zA-Z][_a-zA-Z0-9]* /* C
identifier */
VALUE {NUMBER}|{IDENTIFIER} /* C
value */


/* Unary operators */
UNARY_PREFIX_OPERATORS "+"|"-"|"~"|"!"|"+""+"|"-""-"|"*"|"&"
UNARY_PREFIX_EXPRESSION {UNARY_PREFIX_OPERATORS}{VALUE}
UNARY_POSTFIX_OPERATORS "+""+"|"-""-"
UNARY_POSTFIX_EXPRESSION {IDENTIFIER}{UNARY_POSTFIX_OPERATORS}
UNARY_EXPRESSION
{UNARY_POSTFIX_EXPRESSION}|sizeof{{W}*{VALUE}{W}*}|({W}*TYPE{W}*){W}*{IDENTIFIER}


/* Binary operators */
ARITHMETIC "-"|"+"|"*"|"/"|"%"
BITWISE "|"|"&"|"^"|"~"|"<""<"|">"">"
LOGICAL
"<"|">"|"=""="|"!""="|">""="|"<""="|"&""&"|"|""|"
ASSIGNMENT ({ARITHMETIC}|{BITWISE})"="|"="
BINARY_OPERATOR
{ARITHMETIC}|{BITWISE}|{LOGICAL}|{ASSIGNMENT}
BINARY_EXPRESSION
{VALUE}{W}*{BINARY_OPERATOR}{W}*{VALUE}|{IDENTIFIER}{W}*{ASSIGNMENT}{W}*{VALUE}


/* Ternary operator */
TERNARY_EXPRESSION {VALUE}?{VALUE}:{VALUE}


/* Overall expressions: Still needs recursion */
EXPRESSION
{W}*({VALUE}|{UNARY_EXPRESSION}|{BINARY_EXPRESSION}|{TERNARY_EXPRESSION}){W}*




But, flex complains about unrecognized rules when I try matching
{EXPRESSION} later in the
script. This is my first lex program, and my wish is that anyone here
would point out simple errors that I've made.


~Patrik
[I've never had much luck with complicated named patterns. -John]

Return to the comp.compilers page.
Search the comp.compilers archives again.