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Currying

Currying is about fixing arguments of functions from left to right. It's useful to configurate code and embed parameters that usually serve to define the context of a function execution (i.e. a database connection object). Symbolic functions can be used to reorder arguments if needed.

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// Simple add function
let add x y = x + y

// We fix the first argument to derive the increment function
let inc = add 1

printfn "%d = %d" (inc 5) (add 1 5)

//Can we do the same with subtract?
let sub x y = x - y

let decw = sub 1 // WRONG: this is 1 - y and not x - 1!

printfn "%d = %d" (decw 5) (sub 1 5)

// Let's define a function that reorder arguments
let invert2 f y x = f x y

let dec = invert2 sub 1

printfn "%d = %d" (dec 5) (sub 5 1)
val add : x:int -> y:int -> int

Full name: Script.add
val x : int
val y : int
val inc : (int -> int)

Full name: Script.inc
val printfn : format:Printf.TextWriterFormat<'T> -> 'T

Full name: Microsoft.FSharp.Core.ExtraTopLevelOperators.printfn
val sub : x:int -> y:int -> int

Full name: Script.sub
val decw : (int -> int)

Full name: Script.decw
val invert2 : f:('a -> 'b -> 'c) -> y:'b -> x:'a -> 'c

Full name: Script.invert2
val f : ('a -> 'b -> 'c)
val y : 'b
val x : 'a
val dec : (int -> int)

Full name: Script.dec
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Link:http://fssnip.net/I
Posted:6 years ago
Author:Antonio Cisternino
Tags: currying