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