Re: Some syntax troubles
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- Subject: Re: Some syntax troubles
- From: Thomas Wrensch <twrensch@...>
- Date: 2006年3月16日 20:28:30 +0000 (UTC)
I'm trying to create a small local DSL for one of my tables in following form:
local Foo =
{
["Alpha"] = { op1 "a", op2 "b" };
["Beta"] = { op2 "a", op1 "b", op3 "c" };
}
I need to declare opN functions somewhere. As they wouldn't be used in
such context anywhere else, and they should have convenient short and
common names, I want to have their scope as local as possible.
<...snip...>
Two approaches to think about:
(1) If you can get something to execute before the table evaluator is
initialized, then you can use the setfenv or similar trick. Here's
some code that seems to work:
-- A few functions to set/unset an environment:
function using(env)
local mt = getmetatable(_G)
if not mt then
mt = {}
setmetatable(_G,mt)
end
mt.__index = env
end
function stopusing()
local mt = getmetatable(_G)
if mt then mt.__index = nil end
end
-- Create an environment somewhere
myenv = {}
myenv.op1 = function(y) print("op1:",y) end
myenv.op2 = function(y) print("op2:",y) end
-- Now use it
using(myenv)
local Foo = {
["Alpha"] = {op1 "a"};
["Beta"] = {op1 "a", op2 "b"};
}
stopusing()
This assumes you are not using the global metatable __index for anything
else.
The other approach is to delay evaluation until you've set up an
environment. The only way I know how t do that is to put the code in to a
string. You can imagine the syntax checking issues.
Something like this should work, though this code is not tested:
-- Build an environment (not differences from above)
myenv = {print=print, error=error} -- others as needed
myenv.op1 = function print("op1",op1) end
myenv.op2 = function print("op2",op2) end
-- New version of function for using an environment
function using(env)
return function(code)
local f = loadstring(code)
setfenv(f,env)
return f()
end
end
-- Now use it
local Foo = using(myenv) [[
["Alpha"] = {op1 "a"};
["Beta"] = {op1 "a", op2 "b"};
]]
Hope this helps!
- Tom