MACROS

   The upper-case letters 'A' to 'W' and the punctuation symbols have a
fixed significance to ECCE.  All the lower-case letters, and the
upper-case letters 'X' to 'Z', are available for definition as macros,
that is as abbreviations for sequences of characters.  So also are the
control keys.



Command and text macros

    The printing keys mentioned have a significance as macros only
 within commands, since in data-entry mode or within text strings they
 stand for themselves.  Any of them may be used in a position where a
 command letter is expected and may stand for any sequence or partial
 sequence of commands.

    The letters 'X' to 'Z' and 'x' to 'z' have two additional
 properties: first, they may be used in a position where a text
 parameter is required; and, second, they may be defined to stand for a
 text sequence appearing in the file being edited, or the secondary
 input file, using the Define Macro ("^") command.

    Initially the lower-case letters 'a' to 'w' are defined to be
 equivalent to their upper-case equivalents.  Where command letters
 appear within a macro definition, it is sensible to use the upper-case
 form if it is intended to utilise the basic meaning of that command
 letter, lest the lower-case form should have been re-defined.



    The control keys are always interpreted as macros, in one of two
 ways, depending on how they have been defined.  One form of definition
 forces interpretation of the sequence of characters for which the key
 stands as a command sequence; the other causes the use of the key to be
 equivalent to typing the characters explicitly as part of the text
 being entered.  The distinction is indicated when defining one of these
 keys by using a colon to define a command sequence and an equals-sign
 to define a direct replacement sequence.

    Note that the content of a command macro is interpreted, not when
 the definition is made, but when the macro is used.


Exclamation-mark in macro
 When an exclamation-mark is used in place of a text parameter within a
 sequence invoked as a command macro, the effect is to cause the actual
 text parameter to be sought at the point following the macro call.
 Here again any of the forms of text parameter -- delimited string, text
 macro letter, ditto, or exclamation mark -- are valid.


Key enquiry command         %Q

    The Special command "%Q" is provided as a way of finding out the
 current significance of any key.  It may be used as a one-shot command
 or to cause entry to Enquiry mode.  The first involves pressing the key
 about which information is required immediately after the "%Q"
 (followed by RETURN if not a control key).  The second is indicated by
 typing just "%Q" followed by RETURN.  In this case the Editor continues
 to prompt for keys to be explained until a colon is typed; as before an
 immediate-action key does not require a following RETURN.

    For any basic editing command letter, a brief indication of the
 meaning of the letter is given.  For a key defined as a macro, the
 current definition of that macro is printed out; for a multi-line
 sequence, only the first line is printed out.


Key definition command      %K

    The Special command "%K" is used to define or re-define keys.  Like
 "%Q," it may be used as a one-shot command or to enter a Key-definition
 mode.  In the first case, a single definition is entered along with the
 "%K", while in the definition mode, the Editor continues to prompt for
 definitions until a colon is typed.

    Each definition takes the form of the key to be defined followed by
 a colon or equals sign followed by the text making up the definition.
 When a control key is being defined, depression of the control key in
 the course of the definition causes an asterisk to be echoed.  Use of
 the colon rather than equals-sign as separator indicates that a control
 key is being defined to stand for a command sequence rather than a
 direct replacement text string.

    To cover the case where it is realised after typing in a command
 that it could usefully have been defined as a macro, an alternative
 form of definition is provided to define the key to be the text of the
 last explicitly typed command line.  This is: key to be defined
 followed by the ditto symbol (").


Use of command macros

    After the definitions
        %K x=F/basically/
        %K y=MR*I/  :
 the following equivalences would apply
        xS/actually/      ->    F/basically/S/actually/
        M-10 x T/y/ I/,/  ->    M-10 F/basically/ T/y/ I/,/
        ycomment/         ->    MR*I/  :comment/

 A command macro letter may abbreviate any initial part of a command
 sequence; the last example illustrates a case where it includes the
 opening delimiter for a text string and a fixed initial part.  The
 effect of typing a macro character (letter or control key) is always
 literal substitution of the sequence of characters for which it stands.


 Where a macro letter is defined to be a complete group of two or more
 commands it is always sensible to include parentheses in the
 definition, as in "%K z=(F.error.I.**.)" rather than just "%K
 z=F.error.I.**.", so that if a repetition count is attached to the
 macro letter, it will apply to the whole sequence and not just the last
 component (see next Section).

    The definition of one macro may include a reference to another, but
 any form of circular definition is invalid and an occurrence of any of
 the macro letters within text delimiters always stands for itself.


 One common case where temporary macros can be useful is when some but
 not all occurrences of a text string, say "max", have to be changed to
 something else, say "count", inspection being required to determine
 which.  With the two definitions
         %K x=F/max/
         %K y=S/count/x
 "x" can be used to find the first occurrence of "max" and thereafter
 "y" or "x" depending on whether a change is required or not.

    Macro definitions persevere until the end of the editing session or
 until the relevant key is re-defined.