Function take_while_slice

pub fn take_while_slice<I, F>(input: &mut Pear<I>, f: F) -> Result<I::Slice, I>
where
    I: Input,
    F: FnMut(&I::Slice) -> bool,

Consumes tokens while cond matches on a continously growing slice beginning at a length of 0 and ending when cond fails. Returns the slice between 0 and cond failing. Errors if no such slice exists.