Retro1.org codex

&DATATYPE FUNCTION                                       EXEC built-in function

Use the &DATATYPE function to determine whether the value of the specified
token is alphabetic or numeric data.  The format of the &DATATYPE function is:
+-----------+-----------------------------------------------------------------+
| &DATATYPE | token                                                           |
+-----------+-----------------------------------------------------------------+
where:

token    specifies the target token that is to be examined for alphabetic or
         numeric data.  The result of the &DATATYPE function is NUM or CHAR,
         depending on the data type of the specified token.  This function is
         valid only on the right-hand side of an assignment statement.  For
         example:
            &CHECK = &DATATYPE  ABC
            &TYPE &CHECK
         results in the display:
            CHAR
         A null token is considered character data.