OpenLexer supports the following regular expression syntax, compatible with Flex.
| Syntax | Description |
|---|
. | Any character except newline |
[abc] | Character class: a, b, or c |
[a-z] | Range: lowercase letters |
[^abc] | Negated class: not a, b, or c |
[a-zA-Z0-9_] | Combined ranges |
| Syntax | Equivalent |
|---|
[:alpha:] | [a-zA-Z] |
[:digit:] | [0-9] |
[:alnum:] | [a-zA-Z0-9] |
[:space:] | [ \t\n\r\f\v] |
[:upper:] | [A-Z] |
[:lower:] | [a-z] |
Use inside character classes: [[:alpha:]_]
| Syntax | Description |
|---|
* | Zero or more |
+ | One or more |
? | Zero or one |
{n} | Exactly n |
{n,} | n or more |
{n,m} | Between n and m |
| Syntax | Description |
|---|
^ | Start of line |
$ | End of line |
| Syntax | Description |
|---|
(ab) | Group |
a|b | Alternation: a or b |
| Syntax | Description |
|---|
\n | Newline |
\t | Tab |
\r | Carriage return |
\\ | Literal backslash |
\. | Literal dot |
\* | Literal asterisk |
Double-quoted strings match literally:
"while" { return WHILE; }
"==" { return EQ; }
"++" { return INCREMENT; }
Reference definitions with braces:
/* Definition */
DIGIT [0-9]
%%
/* Rule using definition */
{DIGIT}+ { return NUMBER; }
/* Integer literal */
[0-9]+ { return INTEGER; }
/* Floating point */
[0-9]+\.[0-9]+ { return FLOAT; }
/* Identifier */
[a-zA-Z_][a-zA-Z0-9_]* { return IDENTIFIER; }
/* C-style string */
\"([^"\\]|\\.)*\" { return STRING; }
/* Single-line comment */
"//".* { /* skip */ }