I suggest you pick it up, and play around with it. If not, you owe it to yourself and your colleagues to consider it. What is currying, and why is it so damn tasty? To my mind, the two main ones are: Little pieces can be configured and reused with ease, without clutter; Functions are used throughout. Functions through and through Another advantage of this approach is that it encourages the creation of functions; rather than of methods.
For instance, we have the logging function log date, importance, message that formats and outputs the information. The result of curry func call is the wrapper curried that looks like this:.
A function that uses rest parameters, such as f But most implementations of currying in JavaScript are advanced, as described: they also keep the function callable in the multi-argument variant. Currying is a transform that makes f a,b,c callable as f a b c. JavaScript implementations usually both keep the function callable normally and return the partial if the arguments count is not enough. Currying allows us to easily get partials.
We want to make this open-source project available for people all around the world. Also, there is the possibility of more code reuse, since functions taking a single parameter another curried function don't have to match as specifically with all the parameters. The main motivation at least initially for currying was not practical but theoretical. In particular, currying allows you to effectively get multi-argument functions without actually defining semantics for them or defining semantics for products.
This leads to a simpler language with as much expressiveness as another, more complicated language, and so is desirable. When using functional languages it's very convenient that you can partially apply a function.
This is related to Tacit programming see also Pointfree style on Haskell wiki. This style focuses not on values represented by variables, but on composing functions and how information flows through a chain of functions. We can convert our example into a form that doesn't use variables at all:. By simply composing them, we get the result. This is all thanks to currying. The reverse, un-currying, is also useful in some situations. For example, let's say we want to split a list into two parts - elements that are smaller than 10 and the rest, and then concatenate those two lists.
The result is of type [Int],[Int]. Another thing I haven't seen mentioned yet is that currying allows limited abstraction over arity. In each case the type variable c can be a function type so that these functions work on some prefix of their argument's parameter list. Without currying, you'd either need a special language feature to abstract over function arity or have many different versions of these functions specialized for different arities. In both cases, the parentheses in the type signature are optional, but I've included them for clarity's sake.
The essential difference between the two becomes more visible when we specify function application explicitly. Let's define a function not curried that applies its first argument to its second argument:. Now we can see the difference between add1 and add2 more clearly. EDIT: The essential benefit of currying is that you get partial application for free.
Currying is just syntactic sugar, but you're slightly misunderstanding what the sugar does, I think. Taking your example,. That is a function that takes a tuple and adds its elements. Those two functions are actually quite diffent; they take different arguments. If you wanted to sum each tuple in a list, on the other hand, the addTuple function fits perfectly. Curried functions are great where partial application is useful - for example map, fold, app, filter.
Consider this function, that returns the biggest positive number in the list supplied, or 0 if there are no positive numbers:. Partial Function Application is the process of returning a function that takes a lesser number of arguments. If you wanted, you could even partially apply 3 out of 3 arguments and it would return a function that takes no argument.
When binding 1 to x and partially applying that to the above function f x,y,z you'd get:. Now at any point, you can choose to evaluate f , f' or f''. So I can do:. Currying on the other hand is the process of splitting a function into a nested chain of one argument functions. You can never provide more than 1 argument, it's one or zero. Finally, Closure is the process of capturing a function and data together as a single unit.
A function closure can take 0 to infinite number of arguments, but it's also aware of data not passed to it. Meaning that f' can read the value of x that's inside f. Currying, partial application and closures are all somewhat similar in that they decompose a function into more parts.
Currying decomposes a function of multiple arguments into nested functions of single arguments that return functions of single arguments. There's no point in currying a function of one or less argument, since it doesn't make sense. Partial application decomposes a function of multiple arguments into a function of lesser arguments whose now missing arguments were substituted for the supplied value.
Closure decomposes a function into a function and a dataset where variables inside the function that were not passed in can look inside the dataset to find a value to bind against when asked to evaluate. What's confusing about all these is that they can kind of each be used to implement a subset of the others.
So in essence, they're all a bit of an implementation detail. They all provide similar value in that you don't need to gather all values upfront and in that you can reuse part of the function, since you've decomposed it into discreet units. Currying partial application lets you create a new function out of an existing function by fixing some parameters. It is a special case of lexical closure where the anonymous function is just a trivial wrapper which passes some captured arguments to another function.
We can also do this by using the general syntax for making lexical closures, but partial application provides a simplified syntactic sugar. This is why Lisp programmers, when working in a functional style, sometimes use libraries for partial application.
This op macro will make you a function which takes some arguments x y z In many purely functional languages, partial application is ingrained into the syntax so that there is no op operator. To trigger partial application, you simply call a function with fewer arguments than it requires.
Instead of producing an "insufficient number of arguments" error, the result is a function of the remaining arguments. What currying is doing here is transforming a function that takes two agreements into one that only takes one returning a result.
Partial evaluation. Say x on the RHS isn't just a regular int, but instead a complex computation that takes a while to complete, for augments, sake, two seconds. For the above the result of twoSecondsComputation is evaluated every single time.
This means it takes 6 seconds for this computation. The twoSecondsComputation only needs to be evaluated once. To up the scale, replace two seconds with 15 minutes, or any hour, then have a map against numbers. Summary : Currying is great when using with other methods for higher level functions as a tool of partial evaluation.
Its purpose cannot really be demonstrated by itself. I made up a function "curry". In this context, I don't care what kind of logger I get or where it comes from. I don't care what the action is or where it comes from. All I care about is processing my input. The builder variable is a function that returns a function that returns a function that takes my input that does my work.
This is a simple useful example and not an object in sight. Currying is an advantage when you don't have all of the arguments for a function. If you happen to be fully evaluating the function, then there's no significant difference. Currying lets you avoid mentioning not-yet-needed parameters. It is more concise, and doesn't require finding a parameter name that doesn't collide with another variable in scope which is my favorite benefit. For example, when using functions that take functions as arguments, you'll often find yourself in situations where you need functions like "add 3 to input" or "compare input to variable v".
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