Opened 7 months ago

#8258 new bug

GHC accepts `data Foo where` in H2010 mode

Reported by: hvr Owned by:
Priority: low Milestone: 7.8.3
Component: Compiler Version: 7.0.4
Keywords: Cc:
Operating System: Unknown/Multiple Architecture: Unknown/Multiple
Type of failure: GHC accepts invalid program Difficulty: Unknown
Test Case: Blocked By:
Blocking: Related Tickets:

Description

According to the Haskell2010 report,

The grammar productions relevant for data declarations are the following:

topdecl	→ data [context =>] simpletype [= constrs] [deriving]

(from 4.2.1 Algebraic Datatype Declarations)

However, GHC 7.0.4/7.4.2/7.6.3/HEAD all happily compile the following Haskell module without any warning when using -XHaskell2010 -Wall, even though this is not valid Haskell2010 afaik:

module Foo where

data Foo where

The trailing where in the data declaration is not valid Haskell2010 (without language extensions such as GADT).

At the very least, this divergence from the Haskell Report should be mentioned in 14.1.1. Divergence from Haskell 98 and Haskell 2010.

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