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Partial Application

Partial Application

Partial Application is a feature.

Binds one or more arguments to a function, reducing its arity.


Languages with Partial Application include JavaScript, C++, Perl, Scala, Clojure

Example from JavaScript:
const addNumbers = (num1, num2) => num1 + num2 const add5 = num => addNumbers(10, num)
Example from C++:
// http://www.cplusplus.com/reference/functional/bind/ // bind example #include <iostream> // std::cout #include <functional> // std::bind // a function: (also works with function object: std::divides<double> my_divide;) double my_divide (double x, double y) {return x/y;} struct MyPair { double a,b; double multiply() {return a*b;} }; int main () { using namespace std::placeholders; // adds visibility of _1, _2, _3,... // binding functions: auto fn_five = std::bind (my_divide,10,2); // returns 10/2 std::cout << fn_five() << '\n'; // 5 auto fn_half = std::bind (my_divide,_1,2); // returns x/2 std::cout << fn_half(10) << '\n'; // 5 auto fn_invert = std::bind (my_divide,_2,_1); // returns y/x std::cout << fn_invert(10,2) << '\n'; // 0.2 auto fn_rounding = std::bind<int> (my_divide,_1,_2); // returns int(x/y) std::cout << fn_rounding(10,3) << '\n'; // 3 MyPair ten_two {10,2}; // binding members: auto bound_member_fn = std::bind (&MyPair::multiply,_1); // returns x.multiply() std::cout << bound_member_fn(ten_two) << '\n'; // 20 auto bound_member_data = std::bind (&MyPair::a,ten_two); // returns ten_two.a std::cout << bound_member_data() << '\n'; // 10 return 0; }
Example from Perl:
sub first-and-last ( $first, $last ) { say "Name is $first $last"; } my &surname-smith = &first-and-last.assuming( *, 'Smith' ); &surname-smith.( 'Joe' ); # OUTPUT: «Name is Joe Smith␤»
Example from Scala:
def add(x: Int, y: Int) = {x+y}; add(1, _: Int)
Example from Clojure:
(defn fun-full [x y] (+ x y)) (fun-full 2 3) (def fun-half (partial fun-full 2)) (fun-half 3)
multiple-inheritance-feature.html · partial-application-feature.html · pipes-feature.html

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