[GHC] #13097: Num a => Num (Down a)
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ghc-devs at haskell.org
Tue Jan 10 10:32:36 UTC 2017
#13097: Num a => Num (Down a)
-------------------------------------+-------------------------------------
Reporter: Iceland_jack | Owner:
Type: feature request | Status: new
Priority: normal | Milestone:
Component: libraries/base | Version: 8.0.1
Resolution: | Keywords:
Operating System: Unknown/Multiple | Architecture:
| Unknown/Multiple
Type of failure: None/Unknown | Test Case:
Blocked By: | Blocking:
Related Tickets: | Differential Rev(s):
Wiki Page: |
-------------------------------------+-------------------------------------
Description changed by Iceland_jack:
@@ -26,1 +26,0 @@
-
@@ -31,0 +30,8 @@
+
+ with #12363 + #12465
+
+
+ {{{#!hs
+ >>> 10 < @Down{} 20
+ False
+ }}}
New description:
There are many missing instances for `Down`, I happened to need `Num (Down
_)`. It can be derived with GND:
{{{#!hs
newtype Down a = Down a deriving (Eq, Show, Read, Num)
}}}
which let's us write
{{{#!hs
>>> (<) 10 20
True
>>> (<) @(Down _) 10 20
False
}}}
We can of course add instances for `Functor`, `Applicative`, `Monad`,
`MonadFix`, ... I don't know that they would ever get but it wouldn't be
much trouble copying `Identity`, `Dual` instances.
----
With #12363
{{{#!hs
>>> 10 < @(Down _) 20
False
}}}
with #12363 + #12465
{{{#!hs
>>> 10 < @Down{} 20
False
}}}
--
--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13097#comment:3>
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