Type of zippers. A zipper allow to naviguate in a rope in a convenient and efficient manner. Note that a zipper points to a position between two glyphs, not to a glyph, so in a rope of length len there is len + 1 positions.

make_f rope pos creates a new zipper pointing to positon pos of rope.

make_b rope pos creates a new zipper pointing to positon length rope - pos of rope.

Returns the position of the zipper in the rope.

next zipper returns the glyph at the right of the zipper and a zipper to the next position. It raises Out_of_bounds if the zipper points to the end of the rope.

prev zipper returns the glyph at the left of the zipper and a zipper to the previous position. It raises Out_of_bounds if the zipper points to the beginning of the rope.

move n zip moves the zipper by n glyphs. If n is negative it is moved to the left and if it is positive it is moved to the right. It raises Out_of_bounds if the result is outside the bounds of the rope.

at_bos zipper returns true if zipper points to the beginning of the rope.

at_eos zipper returns true if zipper points to the end of the rope.

find_f f zip search forward for a glyph to satisfy f. It returns a zipper pointing to the left of the first glyph to satisfy f, or a zipper pointing to the end of the rope if no such glyph exists.

find_b f zip search backward for a glyph to satisfy f. It returns a zipper pointing to the right of the first glyph to satisfy f, or a zipper pointing to the beginning of the rope if no such glyph exists.

sub zipper len returns the sub-rope of length len pointed by zipper.

slice zipper1 zipper2 returns the rope between zipper1 and zipper2. If zipper1 > zipper2 then this is the same as slice zipper2 zipper1.

The result is unspecified if the two zippers do not points to the same rope.