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var result = function (a) { | |
return function (state) { | |
return { value: a, state: state }; | |
}; | |
}; | |
var sequence = function (/* monadicActions..., continuation */) { | |
var args = [].slice.call(arguments); | |
var monadicActions = args.slice(0, -1); | |
var continuation = args.slice(-1)[0]; | |
return function (state) { | |
var initialState = { values: [], state: state }; | |
var r = monadicActions.reduce(function (state, action) { | |
var result = action(state.state); | |
var values = state.values.concat(result.value); | |
return { values: values, state: result.state }; | |
}, initialState); | |
var values = r.values.filter(function (value) { | |
return value !== undefined; | |
}); | |
return continuation.apply(this, values)(r.state); | |
}; | |
}; | |
var memoize = function (fn) { | |
return function (a) { | |
return function (cache) { | |
if (a in cache) { | |
console.log("Retrieving from cache:", a); | |
return result(cache[a])(cache); | |
} else { | |
// Clone the cache and add the new value to it. | |
var newCache = Object.create(cache); | |
newCache[a] = fn(a); | |
return result(newCache[a])(newCache); | |
} | |
}; | |
}; | |
}; | |
var memo = memoize(function (a) { | |
return a * 2; | |
}); | |
var initialCache = {}; | |
var result0 = memo(5)(initialCache); | |
console.log(result0); | |
var result1 = memo(4)(result0.state); | |
console.log(result1); | |
var result2 = memo(5)(result1.state); | |
console.log(result2); | |
var result3 = memo(4)(result2.state); | |
console.log(result3); | |
// Using the sequence abstraction, which is basically an imitation of | |
// Haskell's do notation. | |
var cacheComputations = sequence( | |
memo(5), | |
memo(4), | |
memo(5), | |
memo(4), | |
function (a, b, c, d) { | |
console.log(a, b, c, d); | |
return result(a * b * c * d); | |
} | |
); | |
console.log( cacheComputations(initialCache) ); |
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