Lugaru's Epsilon
Editor 14.04

Epsilon User's Manual and Reference
   Primitives and EEL Subroutines
      Buffer Primitives
         . . .
         Undo Primitives
         Searching Primitives
         Moving by Lines
         . . .
      Display Primitives
         Creating & Destroying Windows
         Window Resizing Primitives
         Preserving Window Arrangements
         . . .
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Epsilon User's Manual and Reference > Primitives and EEL Subroutines > Buffer Primitives >

Undo Primitives

int undo_op(int is_undo)
user buffer int undo_size;

With a nonzero argument, the undo_op( ) primitive undoes one basic operation like the undo command, described in Undoing. With an argument of zero, it acts like redo. It returns a bit pattern describing what types of operations were undone or redone. The bit codes are defined in codes.h. UNDO_INSERT means that originally an insertion occurred, and it was either undone or redone. The UNDO_DELETE and UNDO_REPLACE codes are similar.

Epsilon groups individual buffer changes into groups, and undoes one group at a time. While saving changes for undoing, Epsilon begins a new group when it redisplays buffers or when it begins a new command in the main loop. The UNDO_REDISP code indicates the former happened, and UNDO_MAINLOOP the latter. UNDO_MOVE indicates movement is being undone, and UNDO_END is used when Epsilon could only undo part of a command. If undo_op( ) returns zero, the buffer was not collecting undo information (see below).

Epsilon automatically starts a new undo group each time it does normal redisplay or passes through its main loop, by calling either the undo_redisplay( ) or undo_mainloop( ) primitives, respectively. You can call either of these primitives yourself to make Epsilon start a new undo group.

In addition to starting a new group, the undo_mainloop( ) primitive also makes the current buffer start to collect undo information. When you first create a buffer, Epsilon doesn't keep undo information for it, so that "system" buffers don't have this unnecessary overhead. Each time it passes through the main loop, Epsilon calls undo_mainloop( ), and this makes the current buffer start collecting undo information, if it isn't already, and if the buffer-specific variable undo_size is nonzero.

int undo_count(int is_undo)

The undo_count( ) primitive takes a parameter that specifies whether undoing or redoing is involved, like undo_op( ). The primitive returns a value indicating how much undoing or redoing information is saved. The number doesn't correspond to a particular number of commands, but to their complexity.

user buffer int undo_flag;

In addition to buffer changes and movements, Epsilon can record other information in its list of undoable operations. Each time you set the undo_flag variable, Epsilon inserts a "flag" in its undo list with the particular value you specify. When Epsilon is undoing or redoing and encounters a flag, it immediately ends the current group of undo operations and returns a code with the UNDO_FLAG bit on. It puts the value of the flag it encountered in the undo_flag variable. The yank-pop command uses flags 1 and 2 for undoing the previous yank.

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