Deriving Show for Word#

{-# LANGUAGE MagicHash #-}
import GHC.Prim
data A = A Word# deriving Show

This works in 7.6.3, but 7.7 gives

    Can't find interface-file declaration for data constructor GHC.Types.W#
      Probable cause: bug in .hi-boot file, or inconsistent .hi file
      Use -ddump-if-trace to get an idea of which file caused the error

The same file works if Word# is replaced by Int#.

Trac metadata

Trac field	Value
Version	7.6.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture

changed weight to 5

added Tbug Trac import labels

Trac metadata

Trac field	Value
Version	7.6.3 → 7.7

changed milestone to %7.8.1

changed weight to 10

assigned to @simonpj

I know what's happening here.

Trac metadata

Trac field	Value
Priority	normal → highest

mentioned in commit de4090bc

closed

Thanks for reporting this.

Simon

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed
Test case	→ deriving/should_run/T8280

mentioned in commit 9d0ae764

There are a few things I'm confused about here.

1. The commit log says "make Word# a wired-in type", but actually it makes Word a wired-in type. (Word# is a primitive type)
2. Why does the example program need to know anything about W#, the constructor for Word, when it only mentioned Word#?
3. Why does Word need to be a wired-in type at all?

1. Sorry
2. See Note [Deriving and unboxed types] in TcDeriv. It should be a bit longer and more explicit.
3. Grep for wordDataCon. I think Word became wired in this commit:

commit 6821c8a47c0fc61a2d989d368f926cc0ded776e9
Author: Ian Lynagh <igloo@earth.li>
Date:   Wed Apr 23 16:11:15 2008 +0000

    Add 123## literals for Word#

Ok, thanks! Make sense now.

With D672 (#10104 (closed)), deriving/should_run/T10104 supersedes deriving/should_run/T8280.

Trac metadata

Trac field	Value
Test case	deriving/should_run/T8280 → deriving/should_run/T10104

added Phighest label