Thanks Eric and Brent,
Even with GADT, it appears that I'd need extra data definitions. I'll go
without GADT then ...
Brent, my use case is not particularly complicated. I am trying to model
the pdf spec - which says that pdf contains Objects that could of of types
Number, String, Name, Array and Dictionary - while array is list of
objects, the Disctionary is a list of tuples (Name, Object) not (Object,
Object) - hence my situation.
Regards,
Kashyap
On Thu, Mar 21, 2013 at 8:58 PM, Brent Yorgey
On Thu, Mar 21, 2013 at 06:18:46PM +0530, C K Kashyap wrote:
Hi,
I have a situation where I need to define a data type T such that
data T = C1 Int | C2 Char | C3 T
However, I want to enforce a constraint that C3 only allows (C2 Char) and not (C1 Int). That is
If C3 should only be able to hold a C2 Char, then why have it hold a T at all? i.e. why not
data T = C1 Int | C2 Char | C3 Char
but I suppose your real problem is probably more complicated, in which case I would recommend using a GADT as others have suggested.
-Brent
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