Changing the Characters Used to Control the Syntax of Group Expressions

A set of ``control characters'' are used to indicate various items of syntax within a group expression. Each group is created with a set of default control characters, but these can be changed by subsequent calls to GRP_SETCC. Each group has its own set of control characters which can be different to those of other groups, and they can be inspected using routine GRP_GETCC. When calling these routines, specific control characters are represented by the following names:

INDIRECTION

- The character used to indicate that the string which follows is not a literal name but is the name of a text file from which further names are to be read. The INDIRECTION control character defaults to ``^''.

COMMENT

- The character used to indicate that the remainder of the group expression (or record within a text file) is a comment and is to be ignored. The COMMENT control character defaults to ``#''.

DELIMITER

- The character used to delimit elements within a group expression. The DELIMITER control character defaults to ``,''.

NAME_TOKEN

- The character used within a modification element as a token for each name in the basis group. The NAME_TOKEN character defaults to ``$*$''.

SEPARATOR

- The character used to separate old and new substitution strings when editing a group of names. The SEPARATOR character defaults to ``$\mid$''.

OPEN_NEST

- The character used to open a nest within a group expression, within which any DELIMITER characters are ignored. The OPEN_NEST character defaults to ``(''.

CLOSE_NEST

- The character used to close a nest within a group expression, within which any DELIMITER characters are ignored. The CLOSE_NEST character defaults to ``)''.

FLAG

- The character which can be used to flag selected group expressions by appending it to the end of the group expression. The presence of the flag is communicated to the calling application by means of the FLAG argument of routines GRP_GROUP and GRP_GRPEX. The FLAG character defaults to ``-''.

OPEN_KERNEL

- The character used to open a kernel within an element. The OPEN_KERNEL character defaults to ``{''.

CLOSE_KERNEL

- The character used to close a kernel within an element. The CLOSE_KERNEL character defaults to ``}''.

NULL

- This is a character which can be assigned to any other control character to suppress use of that control character (see below). The NULL character defaults to ``%''.

ESCAPE

- This is a character which can be used to ``escape'' another control character within a group expression. If a GRP control character is encountered within a group expression, its special meaning is ignored and it is treated literally if it is preceeded by an escape character. Such escape characters are removed before storing the corresponding strings in the returned group (escape character which do not preceed another control character are not removed). Escape characters can themselves be escaped. By default, the escape character is equal to the null character (i.e. escaping is not available by default).