Identifiers.

  1. An identifier is a sequence of alphanumeric characters along with the underscore, ``

    $\displaystyle \_$

    ''. It must begin with a letter. Upper or lower case may be used, and ISETL preserves the distinction. (I.e.:

    a$\displaystyle \_$ good$\displaystyle \_$ thing

    and

    A$\displaystyle \_$ Good$\displaystyle \_$ Thing

    are both legal and are different.)

  2. An identifier serves as a variable and can take on a value of any ISETL data type. The type of a variable is entirely determined by the value that is assigned to it and changes when a value of a different type is assigned to it.