Memory mapping the file doesn't really help an editor much. For one thing you can't have your buffer changing arbitrarily underneath your parse of it. But also

Memory mapping the file doesn't really help an editor much. For one thing you can't have your buffer changing arbitrarily underneath your parse of it. But also in order to have both precise and fast scrolling, especially when syntax highlighting or line wrap is involved (usually you don't want both but you might want one or the other), you need to do at least a superficial parse on the whole thing anyway.