Re: Blocks/Closures in Lua
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- Subject: Re: Blocks/Closures in Lua
- From: "Pedro Miller Rabinovitch" <miller@...>
- Date: 1997年12月29日 12:30:27 -0300
On 28 Dec 97 at 19:24, Steve Dekorte wrote:
> I'm having problems getting Lua to do something like Smalltalk/Self
> blocks.
(...)
> myCollection:do( function myBlock(a) if a:isGreaterThan(24)
> then a:increment() end end )
(...)
> But I get a syntax error when I try to declare a function within a
> function. Is there any way around this syntax error problem?
First of all, I've been told in Lua 3.1 this problem will vanish --
code like that you specified will be feasible.
In the meantime, you can try using strings to define the functions to
be passed. For example,
func_body = "if param1:isGreaterThan(24) then param1:increment() end"
myCollection:do( func_body )
(...)
function myCollection:do ( func_body )
local param1;
param1 = whatever;
dostring( func_body )
end
(Of course, the temporary variable func_body is used here only to
tidy up the code a bit.)
That, of course, requires a specific parameter name to be specified
(in this case, 'param1'). But there's another way to handle it -- you
can specify a full function in the string (with a specific name and
parameter order, but of course, free parameter names). For example:
my_func = [[
function Iterate ( p )
if p:isGreaterThan(24) then
p:increment()
end
end
]]
(I find the [[ .. ]] construction extremely useful for this kind of
thing.)
Now, 'Iterate' is the locked name, and the parameter 'p' could be
named after whatever your heart desired. myCollection:do would look
something like this:
function myCollection:do ( func_body )
local param1;
param1 = whatever;
dostring( func_body )
Iterate( param1 )
end
... or anything like it. Of course, another solution would be for a
second parameter be the function name specifier, but that goes way
over my point.
And here's a suggestion: before executing the dostring, you can check
the parameter type. That way, myCollection:do can receive as
parameter either a string or a function.
Hope this helps.
Pedro
----------------------------------
Pedro Miller Rabinovitch
miller@tecgraf.puc-rio.br
----------------------------------
Worst Vegetable of the Year:
The brussels sprout. This is also the worst vegetable of next
year.
Steve Rubenstein