call/cc in Go

call-with-current-continuation.go

package main

// For lack of actual generics...
type Input interface{}
type Output interface{}

// CallWithCurrentContinuation returns a function k that can be used to invoke a
// continuation-passing-style function f as if it was a direct-style function.
func CallWithCurrentContinuation(f func(input Input, k func(output Output))) func(input Input) Output {
	return func(input Input) Output {
		var wg sync.WaitGroup
		var output Output
		wg.Add(1)
		f(input, func(x Output) {
			output = x
			wg.Done()
		})
		wg.Wait()
		return output
	}
}

func PerformExpensiveComputation(x Input, cb func(y Output)) {
	// ...
	cb(42)
}

var PerformExpensiveComputationSync func(input Input) Output = CallWithCurrentContinuation(PerformExpensiveComputation)