Laws are essentially diffs against the US code. The diff (slip law) is canonical. They are continually compiled into the US code, which can involve deleting or changing text just like a diff, and periodically an edited, annotated code is published. After a certain amount of time, Congress enacts a portion of the published code, making it canonical and overriding any prior slip law.
What we need now is software that reads bills ("in section 123.abc the text 'blah blah' is replaced by 'bleh bleh') and compiles it into before/after views of what the resulting code would be.
I just suggested this, and then scrolled down to find this.
Someone needs to take the plunge and start writing the program; throw it on Github and tell us all about it. I know people who are looking for such a tool.
