Re: Self-awareness of functions?
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- Subject: Re: Self-awareness of functions?
- From: Henk Boom <henk@...>
- Date: 2010年12月30日 12:45:04 -0500
On 30 December 2010 01:22, Steve Litt <slitt@troubleshooters.com> wrote:
> On Thursday 30 December 2010 00:44:22 Henk Boom wrote:
>
>> function recursify(f)
>> local function g(...)
>> return f(g, ...)
>> end
>> return g
>> end
>>
>> fact = recursify(function (self, n)
>> if n == 1 then
>> return 1
>> else
>> return n * self(n-1)
>> end
>> end)
>
> One of the seven wonders of the world is that Lua actually makes that work. I
> can almost, but not quite wrap my head around it. Tomorrow's another day.
>
> Henk -- by what mental process did you devise this solution?
I remembered that you can define a recursive function without mutation
by passing it to itself as a parameter
local fact2 = function (recur, n)
if n == 1 then return 1 else return n * recur(recur, n-1) end
end
local fact = function (n)
return fact2(fact2, n)
end
After that it was just a matter of turning the pattern above into a
general higher-order function, and adding some sugar so that you don't
need to explicitly pass the function to itself in the recursive call.
henk