is there a reason declarative style if are allowed, but not while ?

[user1234]

On Tuesday, 2 March 2021 at 16:24:18 UTC, user1234 wrote:
> [...]
>
> It's also interesting to note that for the IfStatement, a 
> declaration is allowed because from the AST point of view you 
> just need a supplmental storage class.
> So you have a "StorageClass Expression" not  "Expression | 
> VariableDeclaration"

Just ignore this paragraph. Actually there's also a Type allowed 
so it's rather.

   StorageClass? Type? Expression