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index.js
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'use strict';
var Promise = require('bluebird');
//# purep :: a -> Promise a
//.
//. Takes any value, returns a resolved Promise with that value
//.
//. ```js
//. > purep(3).then(console.log)
//. promise
//. 3
//. ```
exports.purep = function(a) {
return Promise.resolve(a);
};
// apply :: (a -> b ... -> n -> x) -> [a, b ... n] -> x
var apply = function(fn) {
return function(args) {
return fn.apply(this, args);
};
};
// id :: a -> a
var id = function(a) {
return a;
};
var slice = Array.prototype.slice;
var toArray = function(a) {
return slice.call(a);
};
var fold = function(iter, initial, arr) {
if (!arr.length) {
return initial;
}
var newInitial = iter(initial, arr[0]);
return fold(iter, newInitial, slice.call(arr, 1));
};
var map = function(f) {
return function(arr) {
return fold(function(memo, item) {
return memo.concat([f(item)]);
}, [], arr);
};
};
var pipe = function() {
var fns = toArray(arguments);
return function(a) {
return fold(function(acc, fn) {
return fn(acc);
}, a, fns);
};
};
//# fmapp :: (a -> b) -> Promise a -> Promise b
//
//. Transforms a Promise of value a into a Promise of value b
//
//. ```js
//. > fmapp(function(a) { return a + 3; }, Promise.resolve(4)).then(console.log)
//. promise
//. 7
//. ```
exports.fmapp = function(fn) {
return function(p) {
return p.then(fn);
};
};
//# sequencep :: Array Promise a -> Promise Array a
//
//. Transforms an array of Promise of value a into a Promise of array of a.
//
//. ```js
//. > sequencep([Promise.resolve(3), Promise.resolve(4)]).then(console.log)
//. promise
//. [3, 4]
//. ```
exports.sequencep = function(arr) {
return Promise.all(arr);
};
//# traversep :: (a -> Promise b) -> Array a -> Promise Array b
//
//. Maps a function that takes a value a and returns a Promise of value b over an array of value a,
//. then use `sequencep` to transform the array of Promise b into a Promise of array b
//
//. ```js
//. > traversep(function(a) { return Promise.resolve(a + 3); })(
//. [2, 3, 4])
//. promise
//. [5, 6, 7]
//. ```
exports.traversep = function(fn) {
return pipe(map(fn), exports.sequencep);
};
//# pipep :: [(a -> Promise b), (b -> Promise c), ... (m -> Promise n)] -> a -> Promise n
//
//. Performs left-to-right composition of an array of Promise-returning functions.
//
//. ```js
//. > pipep([
//. function(a) { return Promise.resolve(a + 3); },
//. function(b) { return Promise.resolve(b * 10); },
//. ])(6);
//. promise
//. 90
//. ```
exports.pipep = function(pipes) {
return function(a) {
return fold(function(accp, fn) {
return accp.then(fn);
}, exports.purep(a), pipes);
};
};
//# liftp :: (a -> b -> ... n -> x) -> Promise a -> Promise b -> ... -> Promise n -> Promise x
//
//. Takes a function so that this function is able to read input values from resolved Promises,
//. and return a Promise that will resolve with the output value of that function.
//
//. ```js
//. > liftp(function(a, b, c) { return (a + b) * c; })(
//. Promise.resolve(3),
//. Promise.resolve(4),
//. Promise.resolve(5));
//. promise
//. 35
//. ```
exports.liftp = function(fn) {
return function() {
return exports.fmapp(apply(fn))(exports.sequencep(toArray(arguments)));
};
};
//# liftp1 :: (a -> b) -> Promise a -> Promise b
//
//. Takes a function and apply this function to the resolved Promise value, and return
//. a Promise that will resolve with the output of that function.
//
//. ```js
//. > liftp1(function(user) {
//. return user.email;
//. })(Promise.resolve({ email: '[email protected]' }));
//. promise
//. ```
exports.liftp1 = exports.fmapp;
exports.liftp2 = exports.liftp3 = exports.liftp4 = exports.liftp5 = exports.liftp;
//# firstp :: Promise a -> Promise b -> Promise a
//
//. Takes two Promises and return the first if both of them are resolved
//. alias <* firstp
//
//. ```js
//. > firstp(Promise.resolve(1), Promise.resolve(2))
//. promise
//. 1
//
//. > firstp(Promise.resolve(1), Promise.reject(new Error(3)))
//. promise
//. Error 3
//. ```
exports.firstp = exports.liftp(id);
var second = function(a, b) { return b; };
//# secondp :: Promise a -> Promise b -> Promise b
//
//. Takes two Promises and return the second if both of them are resolved
//. alias *> secondp
//
//. ```js
//. > secondp(Promise.resolve(1), Promise.resolve(2))
//. promise
//. 2
//
//. > secondp(Promise.resolve(1), Promise.reject(new Error(3)))
//. promise
//. Error 3
//. ```
exports.secondp = exports.liftp(second);
//# filterp :: (a -> Promise Boolean) -> Array a -> Promise Array a
//
//. Takes a predicat that returns a Promise and an array of a, returns a Promise of array a
//. which satisfy the predicate.
//
//. ```js
//. > filterp(function(a) { return Promise.resolve(a > 3); })([2, 3, 4])
//. promise
//. [4]
//. ```
exports.filterp = function(predictp) {
return function(xs) {
return Promise.filter(xs, predictp);
};
};
//# foldp :: (b -> a -> Promise b) -> b -> Array a -> Promise b
//
//. Returns a Promise of value b by iterating over an array of value a, successively
//. calling the iterator function and passing it an accumulator value of value b,
//. and the current value from the array, and then waiting until the promise resolved,
//. then passing the result to the next call.
//.
//. foldp resolves promises sequentially
//
//. ```js
//. > foldp(function(b, a) { return Promise.resolve(b + a); })(1)([2, 3, 4])
//. promise
//. 10
//. ```
exports.foldp = function(fn) {
return function(init) {
return function(arr) {
if (!arr.length) {
return exports.purep(init);
}
return fn(init, arr[0]).then(function(b) {
return exports.foldp(fn)(b)(slice.call(arr, 1));
});
};
};
};
//# mapError :: (Error -> Error) -> Promise a -> Promise a
//
//. Transform the rejected Error.
//
//. ```js
//. > mapError(function(err) {
//. var newError = new Error(err.message);
//. newError.status = 400;
//. return newError;
//. })(Promise.reject(new Error('Not Found')));
//. rejected promise
//. ```
exports.mapError = function(fn) {
return function(p) {
return p.catch(function(error) {
var newError = fn(error);
return Promise.reject(newError);
});
};
};
//# resolveError :: (Error -> b) -> Promise a -> Promise b
//
//. Recover from a rejected Promise
//
//. ```js
//. > resolveError(function(err) {
//. return false;
//. });
//. ```
//. promise
//. false
exports.resolveError = function(fn) {
return function(p) {
return p.catch(fn);
};
};
//# toPromise :: (a -> Boolean) -> (a -> Error) -> a -> Promise a
//
//. Takes a `predict` function and a `toError` function, return a curried
//. function that can take a value and return a Promise.
//. If this value passes the predict, then return a resolved Promise with
//. that value, otherwise pass the value to the `toError` function, and
//. return a rejected Promise with the output of the `toError` function.
//
//. ```js
//. var validateGreaterThan0 = toPromise(function(a) {
//. return a > 0;
//. }, function(a) {
//. return new Error('value is not greater than 0');
//. });
//
//. > validateGreaterThan0(10)
//. promise
//. 10
//.
//. > validateGreaterThan0(-10)
//. rejected promise
//. Error 'value is not greater than 0'
//. ```
exports.toPromise = function(predict, toError) {
return function(a) {
var valid = predict(a);
if (valid) {
return Promise.resolve(a);
} else {
return Promise.reject(toError(a));
}
};
};