# Buggy code
async def menu(
    ctx: commands.Context,
    pages: list,
    controls: dict,
    message: discord.Message = None,
    page: int = 0,
    timeout: float = 30.0,
):
    """
    An emoji-based menu

    .. note:: All pages should be of the same type

    .. note:: All functions for handling what a particular emoji does
              should be coroutines (i.e. :code:`async def`). Additionally,
              they must take all of the parameters of this function, in
              addition to a string representing the emoji reacted with.
              This parameter should be the last one, and none of the
              parameters in the handling functions are optional

    Parameters
    ----------
    ctx: commands.Context
        The command context
    pages: `list` of `str` or `discord.Embed`
        The pages of the menu.
    controls: dict
        A mapping of emoji to the function which handles the action for the
        emoji.
    message: discord.Message
        The message representing the menu. Usually :code:`None` when first opening
        the menu
    page: int
        The current page number of the menu
    timeout: float
        The time (in seconds) to wait for a reaction

    Raises
    ------
    RuntimeError
        If either of the notes above are violated
    """
    if not all(isinstance(x, discord.Embed) for x in pages) and not all(
        isinstance(x, str) for x in pages
    ):
        raise RuntimeError("All pages must be of the same type")
    for key, value in controls.items():
        if not asyncio.iscoroutinefunction(value):
            raise RuntimeError("Function must be a coroutine")
    current_page = pages[page]

    if not message:
        if isinstance(current_page, discord.Embed):
            message = await ctx.send(embed=current_page)
        else:
            message = await ctx.send(current_page)
        # Don't wait for reactions to be added (GH-1797)
        # noinspection PyAsyncCall
        start_adding_reactions(message, controls.keys(), ctx.bot.loop)
    else:
        try:
            if isinstance(current_page, discord.Embed):
                await message.edit(embed=current_page)
            else:
                await message.edit(content=current_page)
        except discord.NotFound:
            return

    try:
        react, user = await ctx.bot.wait_for(
            "reaction_add",
            check=ReactionPredicate.with_emojis(
                tuple(controls.keys()), message, ctx.author
            ),
            timeout=timeout,
        )
    except asyncio.TimeoutError:
        try:
            await message.clear_reactions()
        except discord.Forbidden:  # cannot remove all reactions
            for key in controls.keys():
                await message.remove_reaction(key, ctx.bot.user)
        except discord.NotFound:
            return
    else:
        return await controls[react.emoji](
            ctx, pages, controls, message, page, timeout, react.emoji
        )


# Traceback (RuntimeError)
Traceback (most recent call last):
File "/usr/local/lib/python3.7/dist-packages/discord/ext/commands/core.py", line 79, in wrapped
ret = await coro(*args, **kwargs)
File "/root/.local/share/Red-DiscordBot/cogs/CogManager/cogs/scheduler/scheduler.py", line 325, in showscheduled
await self.task_menu(ctx, tasks)
File "/root/.local/share/Red-DiscordBot/cogs/CogManager/cogs/scheduler/scheduler.py", line 361, in task_menu
await menu(ctx, embeds, controls)
File "/usr/local/lib/python3.7/dist-packages/redbot/core/utils/menus.py", line 64, in menu
raise RuntimeError("Function must be a coroutine")
RuntimeError: Function must be a coroutine

# Fixed code
async def menu(
    ctx: commands.Context,
    pages: list,
    controls: dict,
    message: discord.Message = None,
    page: int = 0,
    timeout: float = 30.0,
):
    """
    An emoji-based menu

    .. note:: All pages should be of the same type

    .. note:: All functions for handling what a particular emoji does
              should be coroutines (i.e. :code:`async def`). Additionally,
              they must take all of the parameters of this function, in
              addition to a string representing the emoji reacted with.
              This parameter should be the last one, and none of the
              parameters in the handling functions are optional

    Parameters
    ----------
    ctx: commands.Context
        The command context
    pages: `list` of `str` or `discord.Embed`
        The pages of the menu.
    controls: dict
        A mapping of emoji to the function which handles the action for the
        emoji.
    message: discord.Message
        The message representing the menu. Usually :code:`None` when first opening
        the menu
    page: int
        The current page number of the menu
    timeout: float
        The time (in seconds) to wait for a reaction

    Raises
    ------
    RuntimeError
        If either of the notes above are violated
    """
    if not all(isinstance(x, discord.Embed) for x in pages) and not all(
        isinstance(x, str) for x in pages
    ):
        raise RuntimeError("All pages must be of the same type")
    for key, value in controls.items():
        maybe_coro = value
        if isinstance(value, functools.partial):
            maybe_coro = value.func
        if not asyncio.iscoroutinefunction(maybe_coro):
            raise RuntimeError("Function must be a coroutine")
    current_page = pages[page]

    if not message:
        if isinstance(current_page, discord.Embed):
            message = await ctx.send(embed=current_page)
        else:
            message = await ctx.send(current_page)
        # Don't wait for reactions to be added (GH-1797)
        # noinspection PyAsyncCall
        start_adding_reactions(message, controls.keys(), ctx.bot.loop)
    else:
        try:
            if isinstance(current_page, discord.Embed):
                await message.edit(embed=current_page)
            else:
                await message.edit(content=current_page)
        except discord.NotFound:
            return

    try:
        react, user = await ctx.bot.wait_for(
            "reaction_add",
            check=ReactionPredicate.with_emojis(
                tuple(controls.keys()), message, ctx.author
            ),
            timeout=timeout,
        )
    except asyncio.TimeoutError:
        try:
            await message.clear_reactions()
        except discord.Forbidden:  # cannot remove all reactions
            for key in controls.keys():
                await message.remove_reaction(key, ctx.bot.user)
        except discord.NotFound:
            return
    else:
        return await controls[react.emoji](
            ctx, pages, controls, message, page, timeout, react.emoji
        )