On 13 May 2012, at 20:29, José Pedro Magalhães wrote:

On Fri, May 11, 2012 at 5:12 PM, "Philip K. F. Hölzenspies" <pkfh@st-andrews.ac.uk> wrote:

However, it turns out that this never leads to an evaluation of extTyNamesLoc. I've come as far as to see that, since "Located a" is a synonym for "GenLocated SrcSpan a", the type we're looking for really has a binary constructor, thus we should use ext2Q.

This made things work: We first modify the function we apply to Located things:

extTyNamesLoc :: (Data loc, Data a) => SrcSpan -> GenLocated loc a -> OccurrenceTable

extTyNamesLoc l (L l' x) = case cast l' of
Just l'' -> extTyNames l'' x
Nothing -> extTyNames l x

Do you really need this? Can't you use the definition of `extTyNamesLoc` shown previously, and redefine `extTyNames` to use `ext2Q`, as in:

As it turns out, yes I do. You had me doubting whether I had tried this, but doing such a thing gives me:

refact.hs:124:72:

Could not deduce (d1 ~ SrcSpan)

from the context (Data a)

bound by the type signature for

extTyNames :: Data a => SrcSpan -> RefCtx -> a -> OccTab

at refact.hs:124:1-91

or from (Data d1, Data d2)

bound by a type expected by the context:

(Data d1, Data d2) => GenLocated d1 d2 -> OccTab

at refact.hs:124:21-88

`d1' is a rigid type variable bound by

a type expected by the context:

(Data d1, Data d2) => GenLocated d1 d2 -> OccTab

at refact.hs:124:21

Expected type: GenLocated d1 d2 -> OccTab

Actual type: Located d2 -> OccTab

In the return type of a call of `extTyNamesLoc'

In the second argument of `ext2Q', namely `extTyNamesLoc l r'