Use foreach count index as variable in pgfplots

I have a beamer frame with an axis environment that contains a foreach loop. I would like to use the count index deriving from such loop as a variable within the loop. Specifically, I need such variable to affect the visibility and label of the plot. I cannot manage to adapt accordingly neither this nor this chunk of code. I provide hereby a minimum (non) working example. The related picture is obtained by running the currently commented line and while not running (commenting) the line above.

\documentclass[beamer]{standalone}\usepackage{pgfplots}\tikzset{    invisible/.style={opacity=0},    visible on/.style={alt={#1{}{invisible}}},    alt/.code args={<#1>#2#3}{%        \alt<#1>{\pgfkeysalso{#2}}{\pgfkeysalso{#3}}    },}\begin{document}\begin{frame}\begin{center}\begin{tikzpicture}\begin{axis}[width=7cm]    \foreach \p [count=\n from 0] in {0.15, 1.15, 2.15} {        \def\pline{(1-(\p*(\x-3))};        \addplot [mark=none, draw=gray, domain=0:4,visible on=<\n>] {\pline} node [pos=0.25] {\n};        %\addplot [mark=none, draw=gray, domain=0:4] {\pline} node [pos=0.25, fill=white] {L};    }\end{axis}\end{tikzpicture}\end{center}\end{frame}\end{document}