Module common_hof

Given a function with N parameters, returns a new function that supports partial application. The new function accepts anywhere from 1 to N parameters. When that function is called with M parameters, where M is less than N, it returns a new function that accepts the remaining parameters. It continues to accept more parameters until all N parameters have been supplied.

This contrived example uses a partially applied function as an predicate, which returns true if an object is found in both arrays.

example

// returns true if an object is in both of the two arrays
function inBoth(array1, array2, object) {
  return array1.indexOf(object) !== -1 &&
         array2.indexOf(object) !== 1;
}
let obj1, obj2, obj3, obj4, obj5, obj6, obj7
let foos = [obj1, obj3]
let bars = [obj3, obj4, obj5]

// A curried "copy" of inBoth
let curriedInBoth = curry(inBoth);
// Partially apply both the array1 and array2
let inFoosAndBars = curriedInBoth(foos, bars);

// Supply the final argument; since all arguments are
// supplied, the original inBoth function is then called.
let obj1InBoth = inFoosAndBars(obj1); // false

// Use the inFoosAndBars as a predicate.
// Filter, on each iteration, supplies the final argument
let allObjs = [ obj1, obj2, obj3, obj4, obj5, obj6, obj7 ];
let foundInBoth = allObjs.filter(inFoosAndBars); // [ obj3 ]

See http://c2.com/cgi/wiki?PatternMatching

This is a conditional construct which allows a series of predicates and output functions to be checked and then applied. Each predicate receives the input. If the predicate returns truthy, then its matching output function (mapping function) is provided with the input and, then the result is returned.

Each combination (2-tuple) of predicate + output function should be placed in an array of size 2: [ predicate, mapFn ]

These 2-tuples should be put in an outer array.

example

// Here's a 2-tuple where the first element is the isString predicate
// and the second element is a function that returns a description of the input
let firstTuple = [ angular.isString, (input) => `Heres your string ${input}` ];

// Second tuple: predicate "isNumber", mapfn returns a description
let secondTuple = [ angular.isNumber, (input) => `(${input}) That's a number!` ];

let third = [ (input) => input === null,  (input) => `Oh, null...` ];

let fourth = [ (input) => input === undefined,  (input) => `notdefined` ];

let descriptionOf = pattern([ firstTuple, secondTuple, third, fourth ]);

console.log(descriptionOf(undefined)); // 'notdefined'
console.log(descriptionOf(55)); // '(55) That's a number!'
console.log(descriptionOf("foo")); // 'Here's your string foo'