2008/2/15 Antoine Latter <aslatter@gmail.com>:
(sent to the list this time)

The problem is in the type-signature for from_seq:

from_seq :: (Sequence seq) => (seq e) -> (t e)

Neither the From_seq class or the type signature of the from_seq
function place any restrictions on the type of e, so the type can be
rewritten as:

from_seq :: forall e seq . Sequence seq => (seq e) -> (t e)

That is, the class explicitly defines from_seq has having norestrictions on e.

Your from_seq' function requires the type e (in the error, e1) to
inhabit IArray a e.

The IArray constraint isn't compatible with the From_seq class
definition.  You may need to explore multi-parameter type classes:
http://en.wikibooks.org/wiki/Haskell/Advanced_type_classes

Does this help?

Yes, this helped.  I added the type variable, e, to my From_seq class and it worked.  Thank you for the explanation.   Here are the changes I made:

class From_seq t e where
    from_seq :: (Sequence seq) => (seq e) -> (t e)

instance From_seq [] e where
    from_seq seq
    | snull seq  = []
    | otherwise = (shead seq) : (from_seq (stail seq))

instance (Ix i, Num i, IArray a e) => From_seq (a i) e where
    from_seq seq = from_seq' seq