20060303a

1 files changed, 59 insertions, 0 deletions

diff --git a/appl/math/fibonacci.b b/appl/math/fibonacci.b
new file mode 100644
index 00000000..af4e769c
--- /dev/null
+++ b/appl/math/fibonacci.b
@@ -0,0 +1,59 @@
+implement Fibonacci;
+
+include "sys.m";
+include "draw.m";
+
+Fibonacci: module
+{
+	init: fn(nil: ref Draw->Context, argv: list of string);
+};
+
+init(nil: ref Draw->Context, nil: list of string)
+{
+	sys := load Sys Sys->PATH;
+	for(i := 0; ; i++){
+		f := fibonacci(i);
+		if(f < 0)
+			break;
+		sys->print("F(%d) = %d\n", i, f);
+	}
+}
+
+FIB: exception(int, int);
+HELP: con "help";
+
+NOVAL: con -1000000000;
+
+fibonacci(n: int): int
+{
+	{
+		fib(1, n, 1, 1);
+	}
+	exception e{
+		FIB =>
+			(x, nil) := e;
+			return x;
+		* =>
+			return NOVAL;
+	}
+	return NOVAL;
+}
+
+fib(n: int, m: int, x: int, y: int) raises (FIB)
+{
+	if(n >= m)
+		raise FIB(x, y);
+
+	{
+		fib(n+1, m, x, y);
+	}
+	exception e{
+		FIB =>
+			(x, y) = e;
+			x = x+y;
+			y = x-y;
+			raise FIB(x, y);
+		* =>
+			raise HELP;
+	}
+}