问题
Is it possible to define my own infix function/operator in CoffeeScript (or in pure JavaScript)? e.g. I want to call
a foo b
or
a `foo` b
instead of
a.foo b
or, when foo is global function,
foo a, b
Is there any way to do this?
回答1:
ES6 enables a very Haskell/Lambda calculus way of doing things.
Given a multiplication function:
const multiply = a => b => (a * b)
You can define a doubling function using partial application (you leave out one parameter):
const double = multiply (2)
And you can compose the double function with itself, creating a quadruple function:
const compose = (f, g) => x => f(g(x))
const quadruple = compose (double, double)
But indeed, what if you would prefer an infix notation? As Steve Ladavich noted, you do need to extend a prototype.
But I think it can be done a bit more elegant using array notation instead of dot notation.
Lets use the official symbol for function composition "∘":
Function.prototype['∘'] = function(f){
return x => this(f(x))
}
const multiply = a => b => (a * b)
const double = multiply (2)
const doublethreetimes = (double) ['∘'] (double) ['∘'] (double)
console.log(doublethreetimes(3));
回答2:
Actually adding this as an answer: no, this is not possible.
It's not possible in vanilla JS.
It's not possible in CoffeeScript.
回答3:
You can with sweet.js. See:
- http://sweetjs.org/doc/main/sweet.html#infix-macros
- http://sweetjs.org/doc/main/sweet.html#custom-operators
Sweet.js extends Javascript with macros.
It acts like a preprocessor.
回答4:
This is definitely not infix notation but it's kinda close : /
let plus = function(a,b){return a+b};
let a = 3;
let b = 5;
let c = a._(plus).b // 8
I don't think anyone would actually want to use this "notation" since it's pretty ugly, but I think there are probably some tweaks that can be made to make it look different or nicer (possibly using this answer here to "call a function" without parentheses).
Infix function
// Add to prototype so that it's always there for you
Object.prototype._ = function(binaryOperator){
// The first operand is captured in the this keyword
let operand1 = this;
// Use a proxy to capture the second operand with "get"
// Note that the first operand and the applied function
// are stored in the get function's closure, since operand2
// is just a string, for eval(operand2) to be in scope,
// the value for operand2 must be defined globally
return new Proxy({},{
get: function(obj, operand2){
return binaryOperator(operand1, eval(operand2))
}
})
}
Also note that the second operand is passed as a string and evaluated with eval
to get its value. Because of this, I think the code will break anytime the value of operand (aka "b") is not defined globally.
回答5:
Javascript doesn't include an infix notation for functions or sections for partial application. But it ships with higher order functions, which allow us to do almost everything:
// applicator for infix notation
const $ = (x, f, y) => f(x) (y);
// for left section
const $_ = (x, f) => f(x);
// for right section
const _$ = (f, y) => x => f(x) (y);
// non-commutative operator function
const sub = x => y => x - y;
// application
console.log(
$(2, sub, 3), // -1
$_(2, sub) (3), // -1
_$(sub, 3) (2) // -1
);
As you can see I prefer visual names $
, $_
and _$
to textual ones in this case. This is the best you can get - at least with pure Javascript/ES2015.
来源:https://stackoverflow.com/questions/12350790/is-it-possible-to-define-an-infix-function