Replacing Ty in ExternalCore with IfaceType

[Simon Peyton-Jones]

| > the two languages have a very similar type structure. However, since
| > they have very different term structures, there would be distinct
| > HsExpr and ExtCoreExpr data types.
|
| Really? Simon wrote:

Well what I wrote was this:

| * Add a new sort of binding to the data type HsBind, something like
|       data HsBind id = ... | CoreBind id (ExtCore id)
|
| Here ExtCore is basically the data type Exp in the ExternalCore module, but parameterised over the
| type of identifiers.  So we have
|       data ExtCore id = Var id | Dcon id | Lit Lit ... etc

So yes, as Aaron says, I think you'd probably want a HsSyn datatype for External Core terms, as above and as Aaron suggests. They are typechecked differently than HsExpr, because all binders have an explicit type.  It could be done as a subset of HsExpr, I think, but I'd be inclined to use a separate type.

Simon