ppExpr' prec (ExprUnary op expr)
  = if prec >= unary_prec then parens e else e
   where
    e = text x <> ppExpr' unary_prec expr
    x = lookupOp op unary_op_table
ppExpr' prec (ExprUnary op expr)
  = if prec >= unary_prec then parens e else e
   where
    e = text x <> ppExpr' unary_prec expr
    x = lookupOp op unary_op_table
ppExpr' prec (ExprUnary op expr)
  = if prec >= unary_prec then parens e else e
   where
    e = text x <> ppExpr' unary_prec expr
    x = lookupOp op unary_op_table