lib/metalua/extension/withdo.mlua

-------------------------------------------------------------------------------
-- Copyright (c) 2006-2013 Fabien Fleutot and others.
--
-- All rights reserved.
--
-- This program and the accompanying materials are made available
-- under the terms of the Eclipse Public License v1.0 which
-- accompanies this distribution, and is available at
-- http://www.eclipse.org/legal/epl-v10.html
--
-- This program and the accompanying materials are also made available
-- under the terms of the MIT public license which accompanies this
-- distribution, and is available at http://www.lua.org/license.html
--
-- Contributors:
--     Fabien Fleutot - API and implementation
--
-------------------------------------------------------------------------------

-- RAII in metalua.
--
-- Write:
-- with var_1, var_2... = val_1, val_2... do
--    ...
-- end
--
-- will assign val_n to var_n foreach n, and guaranty that var_n:close() will be called,
-- no matter what, even if the body causes an error, even if it returns, even
-- if another :close() call causes an error, etc. No. Matter. What.

require 'metalua.extension.trycatch'

function withdo_builder (x)
   local names, vals, body = unpack(x)
   for i = #names, 1, -1 do
      local name, val = names[i], vals[i]
      body = trycatch_builder{ { `Set{ {name}, {val} }, body }, -- try-block
                               { }, -- catch-block
                               { +{ print ("closing "..-{`String{name[1]}}) },
                                 `Invoke{ name, `String "close" } } }
   end
   table.insert(body, 1, `Local{ names })
   return body
end

mlp.lexer:add 'with'
mlp.stat:add{
   'with', mlp.id_list, '=', mlp.expr_list, 'do', mlp.block, 'end',
   builder = withdo_builder }