ppr_expr (HsArrForm (HsVar v) (Just _) [arg1, arg2] _)
= sep [pprCmdArg arg1, hsep [pprInfix v, pprCmdArg arg2]]
ppr_expr (HsArrForm op _ args _)
ppr_expr (HsArrForm (HsVar v) (Just _) [arg1, arg2] _)
= sep [pprCmdArg arg1, hsep [pprInfix v, pprCmdArg arg2]]
ppr_expr (HsArrForm op _ args _)