alt :: { LMatch RdrName }
: infixexp opt_sig alt_rhs {% checkPattern $1 >>= \p ->
return (LL (Match [p] $2 (unLoc $3))) }
+ | '!' infixexp opt_sig alt_rhs {% checkPattern $2 >>= \p ->
+ return (LL (Match [LL $ BangPat p] $3 (unLoc $4))) }
alt_rhs :: { Located (GRHSs RdrName) }
: ralt wherebinds { LL (GRHSs (unLoc $1) (unLoc $2)) }