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[REBOL] Re: auto-update engine

From: sunandadh:aol at: 15-Feb-2003 12:52

> Hmm, maybe, but they are only useful when you are using Encap > since the first 500k of the exe are equal. So I wouldn't want to > show them to the world as a generic patch system. :-)
What the rest of us need (possibly -- see end) is a process that will compare Version 1 source with Version 2 source and ship a delta that consists only of the edit instructions to change V1 into V2. A simple algorithm that treated source as separate lines would take the following program and produce a three-line delta file: ======original program====== rebol [] a-func: func [p1 p2][ return p1 * p2 ] print "version 1" print "this is the first beta. May not work very well" print a-func 5 6 =====new version ====== rebol [] a-func: func [p1 p2][ return p1 + p2 ] print a-func 5 6 ======change file====== d [4 5] R 3 " return p1 + p2" I 2 "" A more sophisticated program that looked for runs of identical strings would produce a different (and in this case, shorter) delta file. Such algorithms exist and are easy to implement in Rebol. They are a good way of seeing what has changed between any two versions of a program; and are commonly used in source library management programs to hold only the difference between successive checked-in versions. A full distribution process would also have to handle adding new and deleting old scripts. But before any of us write such a thing, I wonder how many of us have Rebol applications that are so large they need such a distribution method? Sunanda.