1. A method of generating machine-executable instructions for processing a stream of values, the method comprising: receiving a representation of processing to be performed on at least one input stream to produce at least one output stream, the representation including a plurality of operators and data flow between the operators; and compiling the representation into machine-executable instructions that, when executed, perform operations on a value of an input data stream of the at least one input stream, the operations being defined by the plurality of operators being executed to completion in accordance with the data flow.