On Sat, May 30, 2015 at 1:46 PM, Matt Oliveri <atma...@gmail.com> wrote:
> Sounds like we have a misunderstanding alright. I'm gonna get dinner,
> then think of a way to get to the bottom of this.
>
Sounds like. :-)
Let me show the part I don't know how to do in any current language.
Assume we have a templated structure ASTNode<T>. It has a children field.
The intent is that the child field will be some structured type (a record
or a product). Depending on the type T, we want the type of the "child"
field to be different.
I suppose we could do this with a family of AST structures, e.g. where T is
the record type itself. So we might have
struct Expr {
ASTNode<Expr> * e1;
ASTNode<Expr> *e2;
}
struct ASTNode<T> {
... common fields ...
T children;
}
though this doesn't seem to handle any of the "subunion" cases in a way I
can obviously see. Except I'm not sure that we can forward-reference a
template in this way.
Even if we can, it begs the question of how to specialize the member
functions of ASTNode, which need to do different things depending on how T
was instantiated. We really don't want do this by using a distinct function
for each type T. The problem is purely practical: it's an unmaintainable
hairball.
shap
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