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## Reduce
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### Instructions
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Create three functions:
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- `fold` that receives an array, a function and an accumulator, in this order,
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and applies the function in the elements of the array starting on the left.
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- `foldRight` that receives an array, a function and an accumulator, in this order,
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and applies the function in the elements of the array starting on the right.
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- `reduce` that works just like the method `[].reduce` when you don't
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specify an accumulator.
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The arguments should be an array and a function.
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The starting value of your accumulator must be the first value of the array.
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If your array is less than 1 argument you should throw an error.
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- `reduceRight` like reduce, from the last value to the first
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Example:
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```js
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const adder = (a,b) => a + b
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fold([1,2,3], adder, 2) // returns 8 (2 + 1 + 2 + 3)
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foldRight([1,2,3], adder, 2) // returns 8 (2 + 3 + 2 + 1)
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reduce([1,2,3], adder) // returns 6 (1 + 2 + 3)
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```
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The use of `[].reduce` and `[].reduceRight` is forbidden for this exercise.
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### Notions
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- [devdocs.io/javascript/global_objects/array/reduce](https://devdocs.io/javascript/global_objects/array/reduce)
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### Code provided
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```js
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Array.prototype.reduce = undefined
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Array.prototype.reduceRight = undefined
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```
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