Bang patterns bind... unexpectedly. Deserves loud warning

Consider the following,

{-# LANGUAGE BangPatterns #-}
hello :: [Int] -> ()
hello (!x:xs) = ...

To me it seems like the bang pattern should be applied to x; but it's not! In fact, this program is equivalent to,

hello (!(x:xs)) = ...

This strikes me as quite surprising, yet there is no mention of how ! is supposed to bind in the users guide nor the Haskell Prime proposal.

This behavior is slightly less surprising if you consider that the bang pattern !Just x is equivalent to !(Just x) (although this also strikes me as a bit unfortunate, although it is likely too late to do much about this).

In sum: We need to document the current syntactic binding properties of ! in the users guide.

Trac metadata

Trac field	Value
Version	7.10.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Documentation
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