def compute_value(v, f):
    """
    Return the value of ``f`` at ``v``.

    INPUT:

    - ``v`` -- a function field valuation on `F`
    - ``f`` -- an element of `F`

    OUTPUT: The value of ``f`` at the point corresponding to ``v``.

    This is either an element of the residue field of the valuation ``v``
    (which is a finite extension of the base field of `F`), or `\\infty`.

    """
    from sage.rings.infinity import Infinity
    if v(f) < 0:
        return Infinity
    else:
        return v.reduce(f)
