CODEWITHSUNDEEP
f#functional-programmingfunctionmethods
J Cooper
J Cooper

Reputation: 17051

Point-free style with objects/records in F#

I'm getting stymied by the way "dot notation" works with objects and records when trying to program in a point-free functional style (which I think is a great, concise way to use a functional language that curries by default).

Is there an operator or function I'm missing that lets me do something like: (.) object method instead of object.method?

(From what I was reading about the new ? operator, I think it works like this. Except it requires definition and gets into the whole dynamic binding thing, which I don't think I need.)

In other words, can I apply a method to its object as an argument like I would apply a normal function to its argument?

Upvotes: 3

Views: 1105

Answers (2)

Brian
Brian

Reputation: 118865

Short answer: no.

Longer answer: you can of course create let-bound functions in a module that call a method on a given type... For example in the code

let l = [1;2;3]
let h1 = l.Head 
let h2 = List.hd l

there is a sense in which "List.hd" is the version of what you want for ".Head on a list". Or locally, you can always do e.g.

let AnotherWay = (fun (l:list<_>) -> l.Head)
let h3 = AnotherWay l

But there is nothing general, since there is no good way to 'name' an arbitrary instance method on a given type; 'AnotherWay' shows a way to "make a function out of the 'Head' property on a 'list<_>' object", but you need such boilerplate for every instance method you want to treat as a first-class function value.

I have suggested creating a language construct to generalize this:

With regards to language design suggestions, what if

 SomeType..Foo optArgs   // note *two* dots

meant

 fun (x : SomeType) -> x.Foo optArgs

?

In which case you could write

list<_>..Head

as a way to 'functionize' this instance property, but if we ever do anything in that arena in F#, it would be post-VS2010.

Upvotes: 5

Robert
Robert

Reputation: 6437

If I understand your question correctly, the answer is: no you can't. Dot (.) is not an operator in F#, it is built into the language, so can't be used as function.

Upvotes: 2

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