| SetName [ Newline ] | = | [ SetExpression [ Newline ] (+|-) ] ... |
Literal sets of characters are delimited using the square brackets '[' and ']' and pre-defined sets are delimited by the braces '{' and '}'. For instance, the text "[abcde]" denotes a set of characters consisting of the first five letters of the alphabet; while the text "{abc}" refers to a set named "abc".
Sets can then be declared by adding and subtracting previously declared sets and literal sets. The GOLD Builder provides a collection of pre-defined sets that contain characters often used to define terminals..
| Note: | When text is read by the Builder, all characters delimited by single quotes are analyzed as literal strings. In other words, any text delimited by single quotes is considered to be exactly as printed. This allows you to specify characters that would normally be limited by the notation. For instance, when defining a rule, angle brackets are used to delimit nonterminals. By typing '<' and '>', you can specify these two characters without worrying about the system misinterpreting them. A single quote character can be specified by typing a double single quote ''. |
| Declaration | Resulting Set |
|---|---|
| {Bracket} = [']'] | ] |
| {Quote} = [''] | ' |
| {Vowels} = [aeiou] | aeiou |
| {Vowels 2} = {Vowels} + [y] | aeiouy |
| {Set 1} = [abc] | abc |
| {Set 2} = {Set 1} + [12] - [c] | ab12 |
| {Set 3} = {Set 2} + [0123456789] | ab0123456789 |
The following declares a set named "Hex Char" containing the characters that are valid in a hexadecimal number.
| {Hex Char} = {Digit} + [ABCDEF] |
The following declares a set containing the characters that can be placed inside a normal "string". In this case, the double quote is the delimiting character (which it is in most programming languages).
| {String Char} = {Printable} - ["] |