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foldBack argument order
f#javascript

I'm implementing the collection modules methods in javascript for my F# to javascript project and have run into a couple of methods with different argument ordering. This isn't a huge deal, but I'm wondering what the reasoning behind the different argument ordering (as compared to the other collection methods) is.

Thanks

.

I think it's to mirror the computation. E.g. from

[link:msdn.microsoft.com]

fold : ('State -> 'T -> 'State) -> 'State -> 'T list -> 'State

Applies a function to each element of the collection, threading an accumulator argument through the computation. This function takes the second argument, and applies the function to it and the first element of the list. Then, it passes this result into the function along with the second element, and so on. Finally, it returns the final result. If the input function is f and the elements are i0...iN, then this function computes f (... (f s i0) i1 ...) iN.

foldBack : ('T -> 'State -> 'State) -> 'T list -> 'State -> 'State

Applies a function to each element of the collection, threading an accumulator argument through the computation. If the input function is f and the elements are i0...iN then computes f i0 (...(f iN s)).

so that it mirrors the argument order. Also, I think these are the same signatures as in e.g. Haskell.

By on 11/18/2010 10:23 AM ()

Thanks for the explanation. I thought I'd let you know that the documentation for Array.foldBack is slightly confusing because it uses improper argument names.

(fun acc elem -> acc - elem)

should be

(fun elem acc -> elem - acc)

By on 11/18/2010 11:06 AM ()

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