Re: constatnt initialization

Clint Olsen wrote:


> You're going to have to implement type equivalence checking to your
> compiler. There are a couple of ways to do it. The brute force way
> is to write a 'deep' comparison which recursively descends into 'type'
> and compares it against 'expression' at each phase along the way to
> determine that they are assignment compatible. This means, for
> structs (records) comparing each field and ensuring that the number
> and type of each field is compatible with each element in the
> expression, comparing the subtype and number of elements for arrays,
> and then simple checks for the intrinsic types (integer, real, string)
> etc. You walk 'type' to help guide you for what to expect for
> successive elements. If you're writing a recursive descent parser,
> this is pretty straightforward since you'll build the 'type' before
> you parse the expression.


This is straightforward only if there are no cycles in the paths that
the comparator follows. Cycles are quite common; they are usually
introduced through pointers. One way is to break cycles (e.g. at
pointers) and use name equality here. The other is to implement a
comparison algorithm that can handle cycles (it's not that difficult:
you mainly have to keep a record of nodes that you already visited).


Regards,
Jo

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