A semi-lazy parallel map that can be used for pipelining. The map functions are evaluated for the first bufSize elements and stored in a buffer and made available to popFront. Meanwhile, in the background a second buffer of the same size is filled. When the first buffer is exhausted, it is swapped with the second buffer and filled while the values from what was originally the second buffer are read. This implementation allows for elements to be written to the buffer without the need for atomic operations or synchronization for each write, and enables the mapping function to be evaluated efficiently in parallel.