On Fri, Sep 14, 2012 at 2:27 PM, Erik Hesselink <[email protected]> wrote:
> In general, I think you have to work inside an existential. So you
> hide the type of the parsed Term inside an existential. If you want to
> apply functions to this Term, you unpack, call the function, and
> repack.
Maybe I should expand what I mean by this. Let's say you have:
data SomeTerm where
SomeTerm :: Term a -> SomeTerm
Your typecheck function goes:
typecheck :: Exp -> SomeTerm
and you want to apply:
transform :: Term t -> Term t
You should do something like:
f (SomeTerm t) = SomeTerm (transform t)
Or, more generally:
onSomeTerm :: (forall t. Term t -> Term t) -> SomeTerm -> SomeTerm
onSomeTerm f (SomeTerm t) = SomeTerm (f t)
Erik
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