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I am writing a function to find the intersection between two sets.

The non-functional requirements of the assignment include avoiding "side effects".

function intersection(a, b) { return helper(a, b, []); } function helper(a, b, c) { if (a.length == 0) { return c; } if (b.contains(a[0])) { return helper(a.slice(1, a.length), b, c.concat([a[0]])); } return helper(a.slice(1, a.length), b, c); }

Would mutating the argument c in the above code be considered a side effect?

The specific assignment is written in OCaml, so, though the above example is in an imperative language, I want to stay true to the spirit of functional programming.

Please don't provide any alternate solutions to the problem.

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If the helper function mutated the object c (which concat doesn't do in JS), then helper would have that side effect. But overall your intersection function wouldn't have any side effect that I can see, as the c array doesn't exist outside of it.

PS: concat returns a new array every time. The original c array is unchanged.

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