Re: Another example for syntactically lightweight closures
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- Subject: Re: Another example for syntactically lightweight closures
- From: "Alexander Gladysh" <agladysh@...>
- Date: Thu, 7 Feb 2008 14:52:13 +0300
> nice :-)
>
> It's a shame so many places seem to explicitly check the type of
> things...
>
> table.foreach ({1,2 , 5, 9}, "|x|x+1")
> stdin:1: bad argument #2 to 'foreach' (function expected, got string)
>
> blargh...
You've just made every string callable -- both lambda strings and
ordinary strings. How would you ensure type-safety now?
For example:
function call_callback(fn)
assert(type(fn) == "function" or type(getmetatable(fn).__call) ==
"function")
fn(42)
end
call_callback(print) -- OK
call_callback("|x| print(x)") -- OK
call_callback("|x| My checkbox") -- Not OK
local my_variable = print
local my_variable = "Hello?!"
call_callback(my_variable) -- Well, you get the point.
On the other hand, it is not absolutely necessary to use __call()
metamethod -- implicit conversion is almost as good.
print( fun("|x,y| x+y")(2,3) )
You may want to omit braces:
print( fun"|x,y| x+y" (20, 30))
Where fun may be basically the same as the __call() metamethod above.
Alexander.