Does this technique extend to polymophic types?
Yes, of course. The type F a b in the earlier message was polymorphic.
Let's say we have the following type:
data D a = C | D a
Is it possible to index the type D a?
I have just lifted the polymorphic Maybe -- which is isomorphic to
your
[EMAIL PROTECTED] wrote:
... loads of cunning stuff omitted
Software-engineering-wise your approach suffers
from an important weakness: a closed world assumption.
The programmer has to maintain your TI and pass it
on in all kinds of contexts for the array of types to
be handled. I also had a
I admire the elegancy of your code which makes the changes to add new data
types minimum. There is one question I want to ask: Does this technique
extend to polymophic types?
Let's say we have the following type:
data D a = C | D a
Is it possible to index the type D a? Or there is some
This message describes functions safeCast and sAFECoerce implemented
in Haskell98 with common, pure extensions. The functions can be used
to 'escape' from or to existential quantification and to make
existentially-quantified datatypes far easier to deal with. Unlike
Dynamic, the present approach
Throughout this message you imply, if not outright state, that Dynamics
requires unsafeCoerce/unsafePerformIO. This is simply not the case.
GHC implements Dynamics with unsafeCoerce, or did last time I checked,
but it can easily be implemented using only existentials. (I presume
that this
