Epsilon User's Manual and Reference >
Primitives and EEL Subroutines >
Buffer Primitives >
user buffer int narrow_start;
user buffer int narrow_end;
int narrow_position(int p) /* buffer.e */
Epsilon provides two primitive variables, narrow_start and
narrow_end, that restrict access to the current buffer. The
commands narrow-to-region and widen-buffer, described
in Miscellaneous, use these variables. Epsilon ignores
the first narrow_start characters and the last narrow_end
characters of the buffer. Usually, these variables have a value of
zero, so no such restriction takes place. Characters outside of the
narrowed region will not appear on the screen, and will remain
outside the control of normal Epsilon commands.
If you try to set a primitive variable such as point to a
position outside of the narrowed area, Epsilon will change the value
to one inside the narrowed area. For example, suppose the buffer
contains one hundred characters, with the first and last ten
characters excluded, so only eighty appear on the screen.
In this case, size( ) will return one hundred, and
narrow_start and narrow_end will each have a value of ten.
point = 3; will give point a value of ten (the
closest legal value), while the statement
point = 10000; will
give point the value ninety. Epsilon adjusts the parameters of
primitive functions in the same way. Suppose, in the example above,
you try to delete all the characters in the buffer, using the
delete( ) primitive. Epsilon would take the statement
delete(0, size()); and effectively change it to
delete(10, 90); to delete only the characters inside
the narrowed area.
The narrow_position( ) subroutine returns its argument
adjusted so that it's inside the narrowed buffer boundaries.
Writing the buffer to a file ignores narrowing. Reading a file into
the buffer lifts any narrowing in effect by setting narrow_start
and narrow_end to zero.
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