Issue 209 - ndmitchell - cannot derive Data instance for ModuleName

Issue 209:	cannot derive Data instance for ModuleName	‹ Prev 6 of 107 Next ›
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Status:	Fixed
Owner:	----
Type-Defect
Priority-Medium
Proj-Derive

Reported by explicitcall, Aug 04, 2009

when compiling

{-# LANGUAGE TemplateHaskell #-}
import Data.Data
import Data.DeriveTH
import Distribution.ModuleName

$(derive makeData ''ModuleName)

I get 

Not in scope: data constructor `ModuleName'

This is reproducible with derive 2.0 as it is with derive 0.1.4

Comment 1 by ndmitchell, Aug 05, 2009

You can't do this because ModuleName is exported abstractly, so the generated 
definition can't be spliced in as it refers to the hidden constructor name.

One option would be to define gfoldl k r x = r x, so you can't use SYB to operate 
inside ModuleName, but you can construct values containing ModuleName and still derive 
Data on them. Would that meet your needs?

Labels: Proj-Derive

Comment 2 by ndmitchell, Aug 06, 2009

With the darcs version of derive you can do:

$(derive makeDataAbstract ''ModuleName)

That should work - if it doesn't let me know.

Status: Fixed