I think this is unnecessary. `usedVariable.node` should be pointing to declaration of a given variable, you should be able to just do a check like this:
```
if (usedVariable.node.parent.type !== "FunctionExpression" && usedVariable.node.parent.type !== "FunctionDeclaration") {
    return;
} else {
    //iterate through children of node.parent.params until you find current node, and mark them as used
}
```
if variable declaration is not part of the params array in a functional declaration or expression, you should just be able to skip it, nothing needs to be marked (at least I think so).