Re: Semantical checks that involve flow of execution of the program

On Sun, 17 Oct 2004 16:09:46 -0400, Lujop wrote:


> //var a is not inicialized
> ...
> if codition1 then
> a <- 1
> else if codition2 then
> b <-2
> else
> a <- 1
>
> With this example Java says that 'a' is possibly not initialized
> because branch 2 don't assign any value in a.


If your representation is a node


Cond (c,yes,no)


then you can just use


a_is_init (yes) and a_is_init (no)


For sequential statements:


Seq(first,next)


you can use


a_is_init(first) or a_is_init(next)


These are synthetic attributes -- you can calculate bottom up
directly in the parser, or using simple recursive descent.


In practice you would not use a function just checking for
one variable 'a'. Instead, you'd calculate *all* the variables
initialised at once, using a set. Then the rules would be like:


init (Cond (c, yes, no) ==> init(yes) intersect init (no)

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