... | @@ -202,3 +202,22 @@ instance Applicative G where |
... | @@ -202,3 +202,22 @@ instance Applicative G where |
|
|
|
|
|
|
|
|
|
There's no way to usefully interact with the `GInt` constructor and get the code to type-check. Thus, I believe (but haven't yet proved), that using GND with `Traversable` is safe, because the `f` in `traverse` can't ever do bad things with its argument. If you, the reader, have more insight into this (or a counterexample!), please write!
|
|
There's no way to usefully interact with the `GInt` constructor and get the code to type-check. Thus, I believe (but haven't yet proved), that using GND with `Traversable` is safe, because the `f` in `traverse` can't ever do bad things with its argument. If you, the reader, have more insight into this (or a counterexample!), please write!
|
|
|
|
|
|
|
|
# Changing default role to nominal
|
|
|
|
|
|
|
|
|
|
|
|
In GHC 7.8, unannotated datatype parameters default to phantom. This means that most normal parameters are given a representational role. It has been argued that perhaps nominal is a better (safer) default, and that users should specify representational when they want it. The problem with a nominal default is that it breaks all current usages of GND by default. Furthering the problem, when a user is unable to use GND it's the *library* that has to change, not the user's code.
|
|
|
|
|
|
|
|
|
|
|
|
On Mar 31, 2014, Dominique Devriese writes the following suggestion:
|
|
|
|
|
|
|
|
|
|
|
|
What I was wondering about is if the dilemma could be solved by
|
|
|
|
choosing nominal-by-default in the long term for the role inference
|
|
|
|
(so that library writers cannot accidentally leave abstraction holes
|
|
|
|
open by forgetting to add role annotations) and use them in the
|
|
|
|
long-term-supported SafeNewtypeDeriving extension, but provide a
|
|
|
|
deprecated not-quite-as-safe GND extension for helping out users of
|
|
|
|
libraries that have not yet added role annotations. I would fancy that
|
|
|
|
this not-quite-as-safe GND could use unsafeCoerce wherever the safe
|
|
|
|
one would give an error about annotated roles. |