[bitc-dev] Static initializer expressions

[Jonathan S. Shapiro]

On Thu, 2008-03-27 at 15:45 -0400, Swaroop Sridhar wrote:
> Jonathan S. Shapiro wrote:
> > SHORT TERM
> > 
> > The following are valid initializer expressions:
> > 
> >   1. Literals
> >   2. Application of +, -, *, /, OR, AND, IF, where the constituent
> >      expressions are initializer expressions.
> >   3. SIZEOF
> >   4. Constructing forms
> >   5. Lambda forms. Note that these cannot be applied at initialization
> >      time because of the limitations of rule [2].
> >   6. Statically initialized symbols whose DEFINITION (not declaration)
> >      are lexically in scope (we say that such a symbol is "observably
> >      defined at initialization time")
> > Does anybody see a problem with the short-term approach above that I may
> > be failing to consider?
> 
> The application of + - * / etc should be permitted only for applications
> on primitive integer types right? Otherwise, the programmer can provide
> an instance for the Arith class where these methods are satisfied
> through side-effecting functions. Such an application should not be 
> permitted even though the arguments are initializer expressions.

I thought I had that covered by [2], but I got it wrong because [4] can
be used to admit new cases. [2] should restrict the set of types over
which the listed operations can be applied.

I suspect that the allowed types should be integral types (including
word), bool, char, string.

I also suspect that there is a longer list of permitted operations that
should be incorporated, but it's easy enough to expand this list as we
discover them.


shap