Question

I was fooling around with some functional programming when I came across the need for this function, however I don’t know what this sort of thing is called in standard nomenclature. Anyone recognizes it?

function WhatAmIDoing(args...)    return function()        return args    end end 

Edit: generalized the function, it takes a variable amount of arguments ( or perhaps an implicit list) and returns a function that when invoked returns all the args, something like a curry or pickle, but it doesn’t seem to be either.

Answer 1

WhatAmIDoing is a higher-order function because it is a function that returns another function.

The thing that it returns is a thunk — a closure created for delayed computation of the actual value. Usually thunks are created to lazily evaluate an expression (and possibly memoize it), but in other cases, a function is simply needed in place of a bare value, as in the case of ‘constantly 5‘, which in some languages returns a function that always returns 5.

The latter might apply in the example given, because assuming the language evaluates in applicative-order (i.e. evaluates arguments before calling a function), the function serves no other purpose than to turn the values into a function that returns them.

WhatAmIDoing is really an implementation of the ‘constantly’ function I was describing. But in general, you don’t have to return just args in the inner function. You could return ‘ackermann(args)‘, which could take a long time, as in…

function WhatAmIDoing2(args...)    return function()        return ackermann(args)    end end 

But WhatAmIDoing2 would return immediately because evaluation of the ackermann function would be suspended in a closure. (Yes, even in a call-by-value language.)