Editing Reduce (computer algebra system) (section)

=== Identifiers and strings ===
Programming languages use [[Identifier (computer languages)|identifiers]] to name constructs such as variables and functions, and [[String (computer science)|strings]] to store text. A REDUCE identifier must begin with a letter and can be followed by letters, digits and underscore characters (<code>_</code>). A REDUCE identifier can also include any character anywhere if it is input preceded by an exclamation mark (<code>!</code>). A REDUCE string is any sequence of characters delimited when input by double quote characters (<code>"</code>). A double quote can be included in a string by entering two double quotes; no other escape mechanism is implemented within strings. An identifier can be used instead of a string in most situations in REDUCE, such as to represent a file name.

REDUCE source code was originally written in all [[Letter case|upper-case]] letters, as were all programming languages in the 1960s. (Hence, the name REDUCE is normally written in all upper-case.) However, modern REDUCE is [[Case sensitivity|case-insensitive]] (by default), which means that it ignores the case of letters, and it is normally written in lower-case. (The REDUCE source code has been converted to lower case.) The exceptions to this rule are that case is preserved within strings and when letters in identifiers are preceded by an exclamation mark (<code>!</code>). Hence, it is conventional to use [[Snake case|snake-case]] (e.g. <code>long_name</code>) rather than [[Camel case|camel-case]] (e.g. <code>longName</code>) for REDUCE identifiers, because camel-case gets lost without also using exclamation marks.