[Haskell-cafe] Embarrassed Haskeller -- why is Read so bad? What are alternatives?

Ryan Newton rrnewton at gmail.com
Tue Oct 15 19:38:14 UTC 2013

Hmm, currently trying to learn how to incorporate DriFT into a cabal
package.  Polyparse doesn't support any other deriving mechanisms does it?
 (GHC.Generics, or TemplateHaskell based, or Neil Mitchell's "derive"

On Tue, Oct 15, 2013 at 3:01 PM, Ryan Newton <rrnewton at gmail.com> wrote:

> Thanks!
> That looks perfect and that is exactly what my googling failed to turn up.
> On Tue, Oct 15, 2013 at 11:49 AM, malcolm.wallace <malcolm.wallace at me.com>wrote:
>> The polyparse package has a complete drop-in replacement for Read, called
>> Text.Parse.  Its lexer is derived closely from Haskell Prelude lex.  It
>> already has instances for all of the standard datatypes, and you can use
>> DrIFT to generate instances for any datatypes outside the usual Prelude
>> types.  The parser is fast, lazy, and space-efficient.  It gives good error
>> messages.
>> Regards,
>>     Malcolm
>> On 15 Oct, 2013,at 04:01 PM, Ryan Newton <rrnewton at gmail.com> wrote:
>> We have great tools for [de]serializing both to binary and to JSON
>> (binary, cereal, json, aeson, etc).  But we have rather weak support for
>> [de]serializing to human readable Haskell-ish external formats.
>> Read instances are both (1) slow, because they take Strings, and (2) they
>> don't allow sensible error messages!  (Historical decision choosing Maybe
>> rather than Either.)
>> Right now I'm working on a project with a Racketeer who is trying to read
>> a 6000 line file as a single list data structure.  The derived Read
>> instance is just telling him it won't parse, with NO error information,
>> line number etc.  To someone used to Scheme readers, that's rather poor.
>> I wish I had something better to tell him!  I am not aware of a library
>> to recommend other than switching to JSON format on disk.  OR manually
>> kludging together a parsing hack that, for example, puts one element of the
>> list on each line and makes much smaller calls to "read".
>> Argh!,
>>   -Ryan
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