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Task/Dragon-curve/Sidef/dragon-curve.sidef

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+define halfpi = Math.pi/2;
+
+# Computing the dragon with a L-System
+var dragon = 'FX';
+{
+    dragon.gsub!('X', 'x+yF+');
+    dragon.gsub!('Y', '-Fx-y');
+    dragon.tr!('xy', 'XY');
+} * 10;
+
+# Drawing the dragon in SVG
+var (x, y) = (100, 100);
+var theta = 0;
+var r = 2;
+
+print <<'EOT';
+<?xml version='1.0' encoding='utf-8' standalone='no'?>
+<!DOCTYPE svg PUBLIC '-//W3C//DTD SVG 1.1//EN'
+'http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd'>
+<svg width='100%' height='100%' version='1.1'
+xmlns='http://www.w3.org/2000/svg'>
+EOT
+
+dragon.each { |c|
+    given(c) {
+        when ('F') {
+            printf("<line x1='%.0f' y1='%.0f' ", x, y);
+            printf("x2='%.0f' ", x += r*Math.cos(theta));
+            printf("y2='%.0f' ", y += r*Math.sin(theta));
+            printf("style='stroke:rgb(0,0,0);stroke-width:1'/>\n");
+        }
+        when ('+') { theta += halfpi }
+        when ('-') { theta -= halfpi }
+    }
+}
+
+print '</svg>';