completed book examples

book/examples/chapter8/Sierpinski.gf

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+concrete Sierpinski of Graftal = {
+  lincat N = {a : Str; b : Str} ;
+  lincat S = {s : Str} ;
+
+  lin z = {a = A; b = B} ;
+  lin s x = {
+    a = x.b ++ R ++ x.a ++ R ++ x.b ; 
+    b = x.a ++ L ++ x.b ++ L ++ x.a
+    } ;
+  lin c x = {s = "newpath 300 550 moveto" ++ x.a ++ "stroke showpage"} ;
+
+  oper A : Str = "0 2 rlineto" ;
+  oper B : Str = "0 2 rlineto" ;
+  oper L : Str = "+60 rotate" ;
+  oper R : Str = "-60 rotate" ;
+}