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// Do works with any Monad that implements the fantasy-land spec | |
// https://github.com/fantasyland/fantasy-land#monad | |
function Do(Type) { return (a, ...fns) => { | |
function doIt(as, fns) { | |
const [fn, ...rest] = fns; | |
if(rest.length === 0) { | |
return as['fantasy-land/chain'](a2s => { | |
return Type['fantasy-land/of'](fn.apply(null, a2s)); | |
}); | |
} else { | |
return as['fantasy-land/chain'](a2s => { | |
const aPrime = fn.apply(null, a2s); | |
return doIt(aPrime['fantasy-land/map']((aP) => [aP, ...a2s]), rest); | |
}); | |
} | |
} | |
return doIt(a['fantasy-land/map'](a2 => [a2]), fns); | |
}} | |
/** | |
* Maybe from https://github.com/origamitower/folktale | |
*/ | |
const Maybe = require('folktale/maybe'); | |
const maybe = | |
Do(Maybe)( | |
Maybe.Just(5), | |
num => Maybe.Just(num * 2), | |
result => result | |
); | |
maybe // folktale:Maybe.Just({ value: 10 }) | |
const maybe2 = Do(Maybe)( | |
Maybe.Just(5), | |
num => Maybe.Nothing(), | |
result => result | |
); | |
maybe2 // folktale:Maybe.Nothing({ }) | |
/** | |
* Async from https://evilsoft.github.io/crocks | |
*/ | |
const Async = require('crocks/Async'); | |
const async = | |
Do(Async)( | |
Async((rej, res) => setTimeout(() => res(5), 1000)), | |
five => Async((rej, res) => setTimeout(() => res(2 * five), 1000)), | |
result => result | |
); | |
async // Async Function | |
async.fork(() => {}, result => { | |
result // 10 | |
}); | |
/** | |
* Chainable Components from https://github.com/pfgray/chainable-components | |
*/ | |
const { ChainableComponent, withState } = require('chainable-components'); | |
const React = require('react'); | |
const composed = | |
Do(ChainableComponent)( | |
withState(3), | |
outer => withState(5), | |
(inner, outer) => ({outer, inner}) | |
) | |
const element = composed.render(({outer, inner}) => ( | |
React.createElement('div', null, `Count is: ${outer.value + inner.value}`) | |
)) | |
element // is now: | |
// <WithState initial={3}> | |
// <WithState initial={5}> | |
// <div>Count is: 8</div> | |
// </WithState> | |
// </WithState> | |
/** | |
* The Function Monad | |
*/ | |
function Func(f) { | |
return { | |
call: f, | |
"fantasy-land/map": g => Func(a => g(f(a))), | |
"fantasy-land/chain": g => { | |
return Func(a => { | |
return g(f(a)).call(a) | |
}) | |
} | |
} | |
} | |
Func["fantasy-land/of"] = function(a) { | |
return Func(() => a); | |
} | |
const identity = x => x; | |
// do { a <- (+1); b <- (* 2); const (a + b) } | |
const wut = | |
Do(Func)( | |
Func(x => x + 1), | |
a => Func(x => x * 2), | |
(a, b) => Func(x => a + b), | |
identity | |
) | |
wut.call(14) // 43 (14+1) + (14*2) |
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