id,summary,reporter,owner,description,type,status,priority,milestone,component,version,resolution,keywords,cc,os,architecture,failure,difficulty,testcase,blockedby,blocking,related
4477,GHC (without -XBangPatterns) silently accepts bang patterns in outermost position,dons,,"GHC 6.8, 6.12, 7.0 at least accept bang patterns on the outside of patterns silently.

{{{
main = do
    let !x = 1
    return ()
}}}

I expect an ""illegal bang pattern"" error, but it is accepted:

{{{

$ ghci A.hs
GHCi, version 7.0.0.20101028: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
Loading package ffi-1.0 ... linking ... done.
[1 of 1] Compiling Main             ( A.hs, interpreted )
Ok, modules loaded: Main.
}}}

However, if we move it inside some parens, it correctly fails:

{{{
main = do
    let (!x) = 1
    return ()
}}}

failing with

{{{

A.hs:2:10:
    Illegal bang-pattern (use -XBangPatterns):
    ! x
}}}",bug,closed,normal,,Compiler (Parser),7.0.1 RC1,fixed,,,Unknown/Multiple,Unknown/Multiple,GHC accepts invalid program,,,,,