sequences.shifted: adding a virtual shifted sequence.

extra/sequences/shifted/authors.txt

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+John Benediktsson

extra/sequences/shifted/shifted-tests.factor

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+! Copyright (C) 2013 John Benediktsson
+! See http://factorcode.org/license.txt for BSD license
+USING: arrays sequences tools.test ;
+IN: sequences.shifted
+
+{ { 1 2 3 7 } } [ 4 iota -1 7 <shifted> >array ] unit-test
+{ { 7 0 1 2 } } [ 4 iota 1 7 <shifted> >array ] unit-test
+{ { 0 1 2 3 } } [ 4 iota 0 f <shifted> >array ] unit-test
+{ { f f f f } } [ 4 iota 4 f <shifted> >array ] unit-test
+{ { f f f f } } [ 4 iota -4 f <shifted> >array ] unit-test

extra/sequences/shifted/shifted.factor

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+! Copyright (C) 2013 John Benediktsson
+! See http://factorcode.org/license.txt for BSD license
+USING: accessors kernel math sequences sequences.private ;
+IN: sequences.shifted
+
+TUPLE: shifted
+{ underlying read-only }
+{ n integer read-only }
+{ fill read-only } ;
+
+C: <shifted> shifted
+
+M: shifted length underlying>> length ;
+
+M: shifted like underlying>> like ;
+
+M: shifted new-sequence underlying>> new-sequence ;
+
+M: shifted nth-unsafe
+    [ n>> neg + ] [ underlying>> ] [ ] tri
+    2over bounds-check? [ drop nth-unsafe ] [ 2nip fill>> ] if ;
+
+M: shifted set-nth-unsafe
+    [ n>> neg + ] [ underlying>> ] bi
+    2dup bounds-check? [ set-nth-unsafe ] [ 3drop ] if ;
+
+INSTANCE: shifted sequence

extra/sequences/shifted/summary.txt

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+Shifted virtual sequences