1. A method of operating a computer comprising: a) providing a compiled code; b) providing logic in the compiled code that causes it to seek to perform an operation for which no compiled code is provided; c) providing a plurality of segments of interpreted code, each segment being adapted to perform a different environment handling operation; d) invoking said interpreted code by an API to perform said different environment handling operations; and e) returning the result of said operation to said compiled code, f) the environment handling operations being performed by constructing models of exceptions in the environment within the interpreted code.