{ "abc" }
[ "abc" sequence>slice >string ] unit-test
+{ t } [ "abcdef" [ 0 3 rot <slice> ] [ 2 4 rot <slice> ] bi slices-overlap? ] unit-test
+{ t } [ "abcdef" [ 0 3 rot <slice> ] [ 1 2 rot <slice> ] bi slices-overlap? ] unit-test
+{ f } [ "abcdef" [ 0 3 rot <slice> ] [ 3 6 rot <slice> ] bi slices-overlap? ] unit-test
+{ t } [ "abcdef" [ 0 3 rot <slice> ] [ 2 4 rot <slice> ] bi slices-touch? ] unit-test
+{ t } [ "abcdef" [ 0 3 rot <slice> ] [ 1 2 rot <slice> ] bi slices-touch? ] unit-test
+{ t } [ "abcdef" [ 0 3 rot <slice> ] [ 3 6 rot <slice> ] bi slices-touch? ] unit-test
+{ f } [ "abcdef" [ 0 3 rot <slice> ] [ 4 6 rot <slice> ] bi slices-touch? ] unit-test
+
+{ "abcdef" } [
+ "abcdef" [ 0 3 rot <slice> ] [ 3 6 rot <slice> ] bi merge-slices >string
+] unit-test
+
+{ "abcdef" } [
+ "abcdef" [ 3 6 rot <slice> ] [ 0 3 rot <slice> ] bi merge-slices >string
+] unit-test
+
+{ "abc" } [
+ "abcdef" [ 0 3 rot <slice> ] [ 0 3 rot <slice> ] bi merge-slices >string
+] unit-test
+
{ "hello" } [ "hello" 0 rotate-headwards ] unit-test
{ "llohe" } [ "hello" 2 rotate-headwards ] unit-test
: sequence>slice ( sequence -- slice )
[ drop 0 ] [ length ] [ ] tri <slice> ; inline
+: slice-order-by-from ( slice1 slice2 -- slice-lt slice-gt )
+ 2dup [ from>> ] bi@ > [ swap ] when ; inline
+
+: ordered-slices-range ( slice-lt slice-gt -- to from )
+ [ to>> ] [ from>> ] bi* ;
+
+: unordered-slices-range ( slice1 slice2 -- to from )
+ slice-order-by-from ordered-slices-range ;
+
+: ordered-slices-overlap? ( slice-lt slice-gt -- ? )
+ ordered-slices-range > ; inline
+
+: unordered-slices-overlap? ( slice1 slice2 -- ? )
+ unordered-slices-range > ; inline
+
+: slices-overlap? ( slice1 slice2 -- ? )
+ unordered-slices-overlap? ;
+
+: ordered-slices-touch? ( slice-lt slice-gt -- ? )
+ ordered-slices-range >= ; inline
+
+: unordered-slices-touch? ( slice1 slice2 -- ? )
+ unordered-slices-range >= ; inline
+
+: slices-touch? ( slice1 slice2 -- ? )
+ unordered-slices-touch? ;
+
+ERROR: slices-don't-touch slice1 slice2 ;
+: merge-slices ( slice1 slice2 -- slice/* )
+ slice-order-by-from
+ 2dup ordered-slices-touch? [
+ [ from>> ] [ [ to>> ] [ seq>> ] bi ] bi* <slice>
+ ] [
+ slices-don't-touch
+ ] if ;
+
: length- ( n sequence -- m ) length swap - ; inline
: rotate-headwards ( seq n -- seq' )