Create variables for old expressions in Boogie #217
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Now each Boogie procedure includes one additional local variable for every global variable in its `modifies` clause, initialized to the initial value of the global at procedure entry. For each such variable `g`, all instances of `old(g)` in the procedure body are replaced with a reference to the new local that stores the old value of `g`. Postconditions still can contain `old(x)` sub-expressions, but they will always be normalized (i.e., `old` will be applied only to variables). Code that interprets postconditions will need to do the appropriate substitution to replace `old` expressions with something else.
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Note: I don't think this is quite done yet. Let's merge #213 first, at the very least.
Now each Boogie procedure includes one additional local variable for every global variable in its
modifiesclause, initialized to the initial value of the global at procedure entry. For each such variableg, all instances ofold(g)in the procedure body are replaced with a reference to the new local that stores the old value ofg. Postconditions still can containold(x)sub-expressions, but they will always be normalized (i.e.,oldwill be applied only to variables).Code that interprets postconditions will need to do the appropriate substitution to replace
oldexpressions with something else.By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.