Re: new thought experiment: what would you add to Lua ?

["John Hind" <john.hind@...>]

At risk of the ire of the old-timers, I'll try bouncing my enhanced 
generic 'for' powerpatch again. The Lua Users WiKi now has a full 
implementation with both code and documentation patches and I have been 
using it myself for years now.

In summary, at present a function is expected after 'for', followed by 
two optional state variables, conventionally supplied by a call to 
'pairs' (or to the 'ipairs' bloat alternative), but you can also write 
your own either on the 'pairs' pattern or as a direct iterator function 
which stores its state in upvalues. My patch provides fallback behaviour 
if presented with a non-function and no further variables. First it 
looks for a metamethod '_iter' and failing that it uses an internal 
implementation of 'pairs'. This enables iteration of objects directly. 
The 'iter' metamethod allows supply of a default iteration method for 
tables and userdata used to implement the OO paradigm while the 'pairs' 
substitute enables quick and easy iteration of anything that can be 
iterated which always works regardless of any messing about with the 
globals (particularly useful in debugging).

With this change, we support a simpler alternative construct which is 
more intuitive and familiar from other languages:

'for my_item in my_collection do print(my_item) end'

whilst preserving Lua's more sophisticated and extensible multi-iterator 
capability. To those who object on 'bloat' grounds, combine with removal 
of 'ipairs' and the 'pairs' and 'ipairs' metamethods and you actually 
have a simplification both conceptually and in implementation.

In all the years I've been pushing this change, I've never seen a 
convincing objection.