Re: getting upvalues in current thread's environment?

[Sam Roberts <sroberts@...>]

On Tue, Jan 16, 2007 at 10:53:47PM -0800, Matthew Armstrong wrote:
> Cool, thanks for your help.
> 
> The reason I asked is I want to try to mimic "eval" functionality, found in
> some other scripting languages, such as perl.
> 
> Lua has loadstring, but this operates in the global environment, and
> afaik/remember, perl puts more context into its eval.

With lua, you put the context in after, with setfenv().

> All I'm really going for here is tighter syntax, as I'm trying to adapt lua
> into a sort of higher level language to suit our purposes.
> 
> For instance, we have a trigger object, which will fire when a certain event
> occurs.  One specialization of the trigger is a conditional version, which
> fires when a particular condition is true.  Creating a conditional trigger
> looks something like this:
> 
> TCond(function() return a > b end)
> 
> but I'd like to shorten it to:
> 
> TCond[[a > b]]

...

> But I'm running into trouble, because loadstring can't access local
> variables 'a' and 'b' in the environment.


Technically, where a and b are isn't an environment, not as lua uses the
term "environment", but instead of making a and b local, and instead of
making them global, put them into a function environment specific
to the evaluation of the condition?

Then the TCond<code> has its own environment it can operate in, you can
specify exactly what will appear there, including preventing global env
access, if you wish.

Clunky example:

  > function f() p = loadstring"print(a)"; setfenv(p, {a='hello',print=print}); p(); end
  > f()
  hello

or

  state = {a=1, b=2}
  function TCond(trigger) condition = loadstring('return '..trigger); setfenv(condition, state) end
  print(condition())

Sam