It’s sort of possible but you need to define the terminating condition because the problem is essentially the same problem as writing a recursive function. The function needs a way to tell whether it should return a function or a value. How you signal the need for values is up to you. One way of … Read more
Understanding higher-order functions Haskell, as a functional language, supports higher-order functions (HOFs). In mathematics HOFs are called functionals, but you don’t need any mathematics to understand them. In usual imperative programming, like in Java, functions can accept values, like integers and strings, do something with them, and return back a value of some other type. … Read more
This turns out to be quite a bit simpler than I initially expected. First we need to define a simple HList, sealed trait HList final case class HCons[H, T <: HList](head : H, tail : T) extends HList { def ::[H1](h : H1) = HCons(h, this) override def toString = head+” :: “+tail.toString } trait … Read more
The below implementation is naive, google for “currying python” for more accurate examples. def curry(x, argc=None): if argc is None: argc = x.func_code.co_argcount def p(*a): if len(a) == argc: return x(*a) def q(*b): return x(*(a + b)) return curry(q, argc – len(a)) return p @curry def myfun(a,b,c): print ‘%d-%d-%d’ % (a,b,c) myfun(11,22,33) myfun(44,55)(66) myfun(77)(88)(99)
scala> val sum2 = (a: Int) => {implicit b: Int => a + b} sum2: (Int) => (Int) => Int = <function1> This will just make b an implicit value for the scope of the function body, so you can call methods that expect an implicit Int. I don’t think you can have implicit arguments … Read more
Java 8 (released March 18th 2014) does support currying. The example Java code posted in the answer by missingfaktor can be rewritten as: import java.util.function.*; import static java.lang.System.out; // Tested with JDK 1.8.0-ea-b75 public class CurryingAndPartialFunctionApplication { public static void main(String[] args) { IntBinaryOperator simpleAdd = (a, b) -> a + b; IntFunction<IntUnaryOperator> curriedAdd = … Read more
@Aadit, I’m posting this because you shared a comment on my answer to To “combine” functions in javascript in a functional way? I didn’t specifically cover currying in that post because it’s a very contentious topic and not really a can of worms I wanted to open there. I’d be wary using the phrasing “how … Read more
It makes you able to do e.g.: scala> def foo(as: Int*)(bs: Int*)(cs: Int*) = as.sum * bs.sum * cs.sum foo: (as: Int*)(bs: Int*)(cs: Int*)Int scala> foo(1, 2, 3)(4, 5, 6, 7, 9)(10, 11) res7: Int = 3906
Let’s first play typechecker for the mechanical proof. I’ll describe an intuitive way of thinking about it afterward. I want to apply (.) to (.) and then I’ll apply (.) to the result. The first application helps us to define some equivalences of variables. ((.) :: (b -> c) -> (a -> b) -> a … Read more
The def declares a method within a surrounding object/class/trait, similar to the way you define methods in Java. You can only use defs within other objects/classes/traits. In the REPL, you cannot see the surrounding object because it’s “hidden”, but it does exist. You cannot assign a def to a value, because the def is not … Read more