#4502: Add a Read instance for Data.Fixed.Fixed
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Reporter: igloo | Owner:
Type: proposal | Status: new
Priority: normal | Milestone: Not GHC
Component: libraries/base | Version: 7.0.1
Keywords: | Testcase:
Blockedby: | Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
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Description changed by igloo:
Old description:
> Add a Read instance for Data.Fixed.Fixed.
>
> Patch and test attached; the essence is:
> {{{
> readsFixed :: (HasResolution a) => ReadS (Fixed a)
> readsFixed = readsSigned
> where readsSigned ('-' : xs) = [ (negate x, rest)
> | (x, rest) <- readsUnsigned xs ]
> readsSigned xs = readsUnsigned xs
> readsUnsigned xs = case span isDigit xs of
> ([], _) -> []
> (is, xs') ->
> let i = fromInteger (read is)
> in case xs' of
> '.' : xs'' ->
> case span isDigit xs'' of
> ([], _) -> []
> (js, xs''') ->
> let j = fromInteger (read js)
> d = 10 ^ genericLength js
> in [(i + (j / d), xs''')]
> _ -> [(i, xs')]
> }}}
>
> Suggested deadline: 1 Dec 2010.
New description:
Add a Read instance for Data.Fixed.Fixed.
Patch and test attached; the essence is:
{{{
readsFixed :: (HasResolution a) => ReadS (Fixed a)
readsFixed = readsSigned
where readsSigned ('-' : xs) = [ (negate x, rest)
| (x, rest) <- readsUnsigned xs ]
readsSigned xs = readsUnsigned xs
readsUnsigned xs = case span isDigit xs of
([], _) -> []
(is, xs') ->
let i = fromInteger (read is)
in case xs' of
'.' : xs'' ->
case span isDigit xs'' of
([], _) -> []
(js, xs''') ->
let j = fromInteger (read js)
l = genericLength js ::
Integer
in [(i + (j / (10 ^ l)),
xs''')]
_ -> [(i, xs')]
}}}
Suggested deadline: 1 Dec 2010.
--
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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4502#comment:1>
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