#5412: dataTypeConstrs gives unhelpful error message
---------------------------------+------------------------------------------
Reporter: NeilMitchell | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: libraries/base | Version: 7.1
Keywords: | Testcase:
Blockedby: | Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
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Old description:
> Take the following program:
>
> {{{
> import Data.Data
> foo = dataTypeConstrs (dataTypeOf (0 :: Int))
> -- raises: *** Exception: Data.Data.dataTypeConstrs
> }}}
>
> The implementation of {{{dataTypeConstrs}}} has the type available as a
> string at this point, so could easily say:
>
> {{{Exception: Data.Data.dataTypeConstrs is not supported for Int, as it
> is not an algebraic data type}}}
New description:
Take the following program:
{{{
import Data.Data
foo = dataTypeConstrs (dataTypeOf (0 :: Int))
-- raises: *** Exception: Data.Data.dataTypeConstrs
}}}
The implementation of {{{dataTypeConstrs}}} has the type available as a
string at this point, so could easily say:
{{{
Exception: Data.Data.dataTypeConstrs is not supported for Int,
as it is not an algebraic data type
}}}
--
Comment(by simonpj):
Good idea! Could you send a patch? Thanks!
Simon
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5412#comment:1>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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