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## [REBOL] What kind of bug is this?

### From: robbo1mark:aol at: 31-Jul-2001 5:35

What kind of bug is this? Ladislav, myself & others have been having a discussion concerning evaluation and self modifying code, and some errors? / very strange behaviour that REBOL displays. Consider the following code in which the block 'a modifies itself at each call by appending + 1 to it's latter series of values. Do'ing this block results in an incrementing sum at each call except when you get to iterations 6, 14 & 30 when some very wierd things start happening. By printing the SUM part of 'a after each call I thought I might be able to deduce the behaviour / evaluation model and predict the result of the next call BUT NO! I'm stumped. Anybody got any explanations? Mark Dickson Heres' the code.............................................
>> a: [ append a [+ 1] 1]
== [append a [+ 1] 1]
>> loop 50 [ print [do a newline] print [remove/part b: copy
a 3 newline]] 1 1 + 1 2 1 + 1 + 1 3 1 + 1 + 1 + 1 4 1 + 1 + 1 + 1 + 1 5 1 + 1 + 1 + 1 + 1 + 1 6 1 + 1 + 1 + 1 + 1 + 1 + 1 8 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 9 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 10 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 11 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 12 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 13 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 14 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 14 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 16 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 17 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 18 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 19 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 20 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 21 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 22 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 1 + 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