Re: Syntax and redundancy

[Rici Lake <lua@...>]

On 30-Aug-05, at 11:22 AM, Chris Marrin wrote:

> I would do it like this:
>
>     local l = { }
>     ... fill the list
>     local p = l
>     while p ~= nil do
>         ...
>         p = p.next
>     end
>
> Any nicer ways?

Write an iterator function.

do
  local function nextlist(field, l)
    return l and l[field]
  end

  function eachlist(l, field)
    field = field or "next"
    return nextlist, field, {[field] = l}
  end
end


list = {"a", next = {"b", next = {"c"}}}
for l in eachlist(list) do print(l[1]) end

-- maybe I didn't want to use "next"
list = {"a", parent = {"b", parent = {"c"}}}
for l in eachlist(list, "parent") do print(l[1]) end

Whether that's nicer or not depends on your perspective, I guess. The 
redundant table constructor is a bit irritating, and in any event it's 
going to be somewhat slower than the while loop. On the other hand, 
it's a nice simple syntax which makes it easy to see what's going on.

(Open to being criticised for doing the Lua equivalent of Boyko's DO 
macro)

R