1 files changed, 83 insertions, 0 deletions
diff --git a/src/pkg/exp/exception/exception.go b/src/pkg/exp/exception/exception.go
new file mode 100644
index 000000000..45e0be3f1
--- /dev/null
+++ b/src/pkg/exp/exception/exception.go
@@ -0,0 +1,83 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This package illustrates how basic try-catch exception handling
+// can be emulated using goroutines, channels, and closures.
+//
+// This package is *not* intended as a general exception handler
+// library.
+//
+package exception
+
+import (
+	"fmt";
+	"runtime";
+)
+
+// A Handler function handles an arbitrary exception value x.
+type Handler func(x interface{})
+
+// An Exception carries an exception value.
+type Exception struct {
+	Value interface{};	// Value may be the nil exception
+}
+
+// Try invokes a function f with a Handler to throw exceptions.
+// The function f may terminate abnormally with an arbitrary
+// exception x by calling throw(x) within f. If an exception is
+// thrown, Try returns an *Exception; otherwise it returns nil.
+//
+// Usage pattern:
+//
+//	if x := exception.Try(func(throw exception.Handler) {
+//		...
+//		throw(42);  // terminate f by throwing exception 42
+//		...
+//	}); x != nil {
+//		// catch exception, e.g. print it
+//		fmt.Println(x.Value);
+//	}
+//
+// Alternative:
+//
+//	exception.Try(func(throw exception.Handler) {
+//		...
+//		throw(42);  // terminate f by throwing exception 42
+//		...
+//	}).Catch(func (x interface{}) {
+//		// catch exception, e.g. print it
+//		fmt.Println(x);
+//	})
+//
+func Try(f func(throw Handler)) *Exception {
+	h := make(chan *Exception);
+
+	// execute try block
+	go func() {
+		f(func(x interface{}) {
+			h <- &Exception{x};
+			runtime.Goexit();
+		});
+		h <- nil;	// clean termination
+	}();
+
+	return <-h;
+}
+
+
+// If x != nil, Catch invokes f with the exception value x.Value.
+// See Try for usage patterns.
+func (x *Exception) Catch(f Handler) {
+	if x != nil {
+		f(x.Value)
+	}
+}
+
+
+func (x *Exception) String() string {
+	if x != nil {
+		return fmt.Sprintf("exception: %v", x.Value)
+	}
+	return "";
+}