Re: Desired Lua Features
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- Subject: Re: Desired Lua Features
- From: Sean Conner <sean@...>
- Date: 2018年1月28日 17:23:01 -0500
It was thus said that the Great KHMan once stated:
>
> I think certain thinking processes when coding translates well to
> a switch/case kind of construct, but it doesn't happen often
> (well, depends). When it happens, the coder stops and asks, why
> can't I use switch/case here?
Talking about switches. One thing I often wish I could do is the
following [1]:
switch(c)
{
case < 0 : /* handle case */
break;
case == 0 : /* handle this case */
break;
case > 0 : /* and this case */
break;
}
I do recall reading about a proposed language back in the mid-80s that
unified if-then with switch (with the added bonus of removing the keywords!)
which is where I got the above. The actual proposal was:
(?var
= value1 : statements ;
= value2 : statements ;
= @ : statements ; /* default value */
?)
A simple 'if' statement would be:
(?var = x : statement ?)
?var = x : statement ;
And this variation:
(?
M = 'C'; 'S' ; 'Q';
^n := 1; 2; 3;
?)
which assigns n depending upon what is in M. There's also Erlang's switch,
whch uses patterns [2] to decide what to do:
case Position of
{ X , Y , Dir } -> do_that();
{ X , Y , Dir , _ , _ } -> do_thing();
{ X , Y , _ , _ , _ } -> do_other();
{ X , Y } -> do_this();
end
where '_' is a "don't care what the value is." A better example would be
this (note: the code was written for a wide window):
scorestrike( [ {First,Second} | _ ]) when First < 10, Second < 10 -> First + Second;
scorestrike( [ {10 , _ } , {Third , _ } | _ ]) when Third < 10 -> 10 + Third;
scorestrike( [ {10 , _ } , {10 , _ } | _ ]) -> 20.
The Erlang compiler will figure out how best to represent that (internally
treated like a series of if/else or a switch or whatever).
-spc (There are a lot of ways to go with this)
[1] Related to that:
0 <= x < 15
but I don't know of any language that supports that type of check.
[2] Not Lua patterns.