Proposal: NF newtype

[Roman Cheplyaka]

On 22/04/15 21:54, Edward Z. Yang wrote:
> But it is an interesting question whether or not 'UnsafeNF' should be
> used, since the value read in is known to be in normal form.

Is it?

newtype X = X Int
  deriving Show
instance Read X where
  readsPrec n = map (first $ X . trace "eval") . readsPrec n

> length (read "[1,2,3]" :: [X])
3
> read "[1,2,3]" :: [X]
[X eval
1,X eval
2,X eval
3]

Or did you mean something else?

> Excerpts from Henning Thielemann's message of 2015-04-22 19:49:56 +0100:
>>
>> On Wed, 22 Apr 2015, Dan Burton wrote:
>>
>>> A hand-written read makes more sense to me in this case:
>>> read = makeNF . read
>>> show = show . getNF
>>
>> Show and Read instances should process Strings representing Haskell code, 
>> and I guess, Haskell code with the same type as the represented value. 
>> Thus the NF should be part of the formatted value.
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