We investigate functional computation as a special form of concurrent computation. As formal basis, we use a uniformly confluent core of the pi-calculus, which is also contained in models of higher-order concurrent constraint programming. We embed the call-by-need and the call-by-value lambda-calculus into the pi-calculus. We prove that call-by-need complexity is dominated by call-by-value complexity. In contrast to the recently proposed call-by-need lambda-calculus, our concurrent call-by-need model incorporats mutual recursion and can be extended to cyclic data structures by means of constraints.