Thanks! I don't have the slightest idea what any of this did, with the exception of "cd Idris-dev", but it seems to have worked...up until I got this message:
 
Populated index cache.    
No compiler found, expected minor version match with ghc-8.0.2 (x86_64) (based on resolver setting in /home/third/Idris-dev/stack.yaml).
To install the correct GHC into /home/third/.stack/programs/x86_64-linux/, try running "stack setup" or use the "--install-ghc" flag.
 
...additionally, I don't seem to have acquired a ~/.local/bin/idris ("no such file or directory"), nor for that matter do I know how to adjust my PATH.
 
Also, for what it may be worth, I had been warned after the "curl -sSL https://get.haskellstack.org/ | sh" that:
 
Detected Linux distribution: linuxmint
This installer doesn't support your Linux distribution, trying generic
bindist...
Stack has been installed to: /usr/local/bin/stack
Since this installer doesn't support your Linux distribution,
there is no guarantee that 'stack' will work at all!  You may
need to manually install some system info dependencies for GHC:
  gcc, make, libffi, zlib, libgmp and libtinfo
Please see http://docs.haskellstack.org/en/stable/install_and_upgrade/
Pull requests to add support for this distro would be welcome!
WARNING: '/home/third/.local/bin' is not on your PATH.
    For best results, please add it to the beginning of PATH in your profile.
 
...Sorry to be so completely clueless about the most basic aspects of what's going on, but it really is the state of my knowledge for now!
 
 
-------------------------
 
Date: Tue, 29 Aug 2017 09:08:35 -0400
From: David McBride <toad3k@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] Installing Idris for Linux Dummies:
"The following packages are likely to be broken..."
Message-ID:
<CAN+Tr41Q_g1WpUgXpzpJgXnKFP8QC6Z1mKyzUurWtx3Pu6cLjg@mail.gmail.com>
Content-Type: text/plain; charset="UTF-8"

The problem most users face with using straight up cabal is that often
the needs of one package conflict with the needs of some of the others
you've installed. I highly recommend you use stack to install idris.
The process should look something like this:

download stack, install it. (directions here:
https://docs.haskellstack.org/en/stable/README/)
git clone https://github.com/idris-lang/Idris-dev.git
cd idris-dev
stack install

And then either run ~/.local/bin/idris or make sure .local/bin is in
your PATH so that you can run idris on the command line.

On Tue, Aug 29, 2017 at 9:02 AM, Manny Romero <mannyromero@mail.com> wrote:
> I am a Linux user (Mint 18) trying to install Idris. I don't know the
> slightest thing about computers. I barely managed to install Linux, and
> later the full GHC, based on ample instructions available on the Web. (Still
> don't actually recall how I did it!)
>
> Idris, however, seems a little trickier. I followed the website
> (https://www.idris-lang.org/download/)'s instructions:
>
> cabal update
> cabal install idris
>
> ...because apparently I installed "cabal" at some point. But I get this
> message, which apparently is quite common:
>
> cabal: The following packages are likely to be broken by the reinstalls:
> semigroupoids-5.1
> lens-4.15.1
> kan-extensions-5.0.1
> profunctors-5.2
> comonad-5
> bifunctors-5.4.1
> Use --force-reinstalls if you want to install anyway.
>
> ...those are some of my favorite things! I can't live without them! I am
> reading things about creating a "sandbox" and so forth. But I cannot use or
> make sense of this information. I don't know the first thing about cabal; I
> never use it; I just load everything into GHCI all the time.
>
> Does anyone have some *specific* instructions that I can follow (as "rotely"
> and dumbly as possible) to get Idris downloaded so I can use it for some
> beginning studies, without breaking Haskell?
>
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> Beginners@haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>