typo

[lambda.git] / installing.mdwn

## Notes ##

*   If the instructions below seem overwhelming, note that it should be possible to do a lot of this course using only demonstration versions of these languages [[that run in your web browser|browser]].

*   We were updating this page vigorously until about 2:30 pm on Saturday 31
January. Now it is relatively stable, but we'll tweak it as we learn more. We
encourage you to try to get the software set up sooner rather than later, and
those who do so first should let us know how things go---whether it's smoothly
or not---so that we might possibly refine or expand the instructions for
others. It'd be great if you took careful notes of what you did, step by step.
If our instructions are broken or misleading or incomplete, and you figure out
how to fix them on your own, it'd also be great if you can tell us what went
wrong and exactly what you did to achieve joy.

*   On a Mac or Linux system, you have a number of *system directories* such as `/usr` and `/Library`,
    and also your *user home directory* which will be named something like `/User/george` or `/home/george`
    if you are `george`. Other ways to refer to the user home directory are as `~` (the tilde character)
    or as `$HOME`. When installing software, you sometimes have a choice of whether to install it into
    the system directories or in subdirectories of your user home. When this choice was available,
    I made the instructions that follow select the latter. This makes it somewhat harder for things
    to get messed up, and makes it somewhat easier for you to remove things later.

    If you're using a Mac without MacPorts (explained below), then Chicken and
    OCaml will be installed under your user home; but Racket's and GHC's
    Installers put them into system directories.


## Identifying your system ##

We'll assume you're using either Mac OS X, or Windows, or Linux.
If you're running **iOS**, you'll have a much harder time (perhaps impossible,
perhaps not) getting this software to run on your machine, and we can't give
you any guidance.

If you're using **Mac OS X**, take note of what version of the Mac OS you're
running. (Under the Apple Menu, select "About this Mac".)

*    Leopard (10.5)
*    Snow Leopard (10.6)
*    Lion (10.7)
*    Mountain Lion (10.8)
*    Mavericks (10.9)
*    Yosemite (10.10)

Furthermore, Mac users will be in one of two subgroups:

*   You'll have Apple's Xcode and the independent MacPorts system
    installed. (Probably you don't. If you don't know what I'm talking about, you don't have these.)

    If you don't have these, but want to try this route, you can read about
    the MacPorts system at <http://www.macports.org/>.
    This automates the building of Unix-type software on your Mac; it
    makes it a lot easier to check for dependencies, use more-recent
    versions of things, and so on. (Though as it happens, MacPorts only has an older version of
    our chosen implementation of Scheme.)

    There are also other package management systems available for the Mac, notably Homebrew and Fink. I only know a little bit about them.

    There are instructions about how to get Xcode on the [Installing MacPorts](https://www.macports.org/install.php) page.
    Some versions of [Xcode](http://developer.apple.com/xcode.html) are available for free on the Mac App Store.
    Other versions are available through Apple's Developer website (some of these are free, but do require you to
    register with Apple as an "Apple Developer", which involves clicking to accept a legal agreement with Apple).
    I have an older version of this installed. If you download a recent version, email me and let me know how the
    process works so I can tell others.
    <!--
    The latest version of Xcode to work with 10.5 / Leopard is 3.14; more recent versions (>= 3.2) require 10.6 / Snow Leopard.
    3.2.6 is last version that can be downloaded for free by users of 10.6 / Snow Leopard. (But if they pay, they can use up to Xcode 4.2.)
    Xcode 4.1 was free to all users of 10.7 / Lion. Is Xcode 4.6.x still available for free? Are Xcode 5.x and/or 6.x available for free?
    -->

*   Or you won't have those installed. (**Most Mac users will be in this group.**)
    Then you'll need pre-packaged (and usually pretty GUI) installers for
    everything. These are great when they're available and kept up-to-date;
    however sometimes those conditions aren't met.



If you're using **Windows**, you'll be in one of two subgroups:

*   You'll have the Cygwin system <http://www.cygwin.com/> installed.
    This puts a Unix-like layer on top of your Windows system,
    and makes it easier for you to use the same software everybody
    else will be using, without its needing as much special-for-Windows
    treatment. However, many of you won't have this installed.

*   You won't have Cygwin installed. (**Most Windows users will be in this group.**)
    You might in theory have a different group of compilers installed
    (MinGW, or Microsoft Visual C++) but we'll assume that the overwhelming
    majority of users in this group don't have access to a compiler and
    need pre-packaged installers for everything.


If you're using **Linux**, you could be using any one of numerous packaging
systems.

*   We'll give examples using the packaging system shared by Debian and Ubuntu,
    and we'll assume that those of you using different packaging systems will know
    how to make the relevant substitutions.


**For everyone**, a general item to take note of is what "processor architecture" your machine is running. Three of the possibilities are:

*   One of Intel's i386, i486, i586, i686 architectures. These are collectively known as "x86" or "IA-32" or sometimes just "32-bit".
*   Intel or AMD's x86\_64 architecture. This is also called "x64" or "amd64" or "IA-64" or sometimes just "64-bit". (Note that these *aren't* "x86" machines, even though "x86\_64" starts with those letters.)
*   ARM or some other architecture. These are generally lower-powered machines, like iPads. Some of the software we're proposing *might* in principle be capable of running on such machines, but installers don't seem to be available. We'll assume you have access to an x86 or x86\_64 machine.

On Linux or Mac OS X, you can open a terminal and type `uname -m`. If the
result is "x86\_64", then you've got x64/64-bit. If it's "i386" or something
like that, then you've got x86/32-bit. I think that Mac OS Xs from 10.7 / Lion
forward have all been x86\_64-only.

On Windows,
[here is a page that can help you figure this out](http://windows.microsoft.com/en-us/windows/32-bit-and-64-bit-windows).
I think that most machines running Windows XP will be x86/32-bit (unless it's
a version of Windows with "64-bit" or "x64" in its title); machines running
Windows Vista or Windows 7 or Windows 8 could be running either x86/32-bit or
x64/64-bit.


## PLEASE REPORT PROBLEMS (AND SOLUTIONS!) ##

We haven't tested these instructions ourselves, and they're not explicit
step-by-step instructions in any case. If you encounter troubles, please email
to let us know so that we can amend the instructions to help others. If you
figure out how to fix the problem youself (and please do), please also write
with suggestions how we can change these instructions to make the process
easier and more straightforward for others.


## Preliminaries ##

If you're using Linux or a Mac without MacPorts, then open a Terminal and type the following. You probably want to copy and paste it to make sure you don't make mistakes:

    (IFS=:; for p in $PATH; do [ /usr/local/bin = "$p" ] && exit 0; done;
            echo 'export PATH="/usr/local/bin:$PATH"' >> ~/.bash_profile)
    mkdir -p ~/bin
    echo 'export PATH="$HOME/bin:$PATH"' >> ~/.bash_profile


<a name=scheme></a>
## Getting Scheme ##

**Scheme** is one of two or three major dialects of *Lisp*, which is a large family
of programming languages. The other dialects are called "Common Lisp" and "Clojure".
Scheme is the more clean and minimalist dialect, and is what's mostly used in
academic circles.

*   In your web browser:

    There is a (slow, bare-bones) version of Scheme available for online use at <http://tryscheme.sourceforge.net/>.

Scheme itself has umpteen different "implementations", which share most of
their fundamentals, but have slightly different extensions and interact with
the operating system differently. One major implementation is called [Racket](http://racket-lang.org),
and that is what we recommend you use. (A few years back they were called PLT Scheme, but then
they changed their name to Racket.)
If you're already using or comfortable with
another Scheme implementation, though, there's no compelling reason to switch.


Another good Scheme implementation is [Chicken](http://www.call-cc.org). For our purposes, this is in some respects
superior to Racket, and in other respects inferior. If you have any issues with installing or using Racket, you could
try this out instead. You might even want to install both.
<!--
Racket doesn't have R7RS-small, and won't anytime soon. :-(
Also Chicken's library collection seems stronger, or at least better organized and maintained.
Other R7RS-friendly: [Gauche](http://practical-scheme.net/gauche), [Chibi](https://code.google.com/p/chibi-scheme).
-->

Racket and Chicken stand to Scheme in something like the relation Firefox stands to HTML. They are two programs (or platforms) among others for working with the Scheme language; and many of those programs (or web browsers) permit different extensions, have small variations, and so on.

Racket has several components. The two most visible components for us are a command-line interpreter named "racket" and a teaching-friendly editor/front-end named "DrRacket". You will probably be working primarily or wholly in the latter.
<!-- "racket" used to be mzscheme, "DrRacket" used to be DrScheme -->

The current version of Racket is 6.1.1 (released November 2014).

*   **To install in Windows**

    Go to <http://racket-lang.org/download/>. Download and install the "Windows x64" version. (Or the "Windows x86" verson if you have an older, 32-bit system.)

*   **To install on Mac without MacPorts**

    Go to <http://racket-lang.org/download/>. Download and install the option for your system, most likely "Macintosh
    OS X (Intel 64-bit)".

    After you copy the files from the Installation disk to your /Applications folder, I think it's helpful to do these additional steps. In a Terminal, type:

        sudo ln -s /Applications/Racket*/DrRacket.app /Applications/
        ln -s /Applications/Racket*/bin/racket ~/bin/

    (If you get an error about ".../bin/: No such file or directory", then you didn't follow the Preliminary instructions above.)

    Then you can launch Racket either by double-clicking the DrRacket icon in
    your Applications folder (this gives you the GUI interface); or by typing
    `racket` in a Terminal (this gives you the command-line version).

    Instead of, or in addition to, the first line above, you could drag the *DrRacket.app* icon to your Dock.

*   **To instead install Chicken Scheme on Mac without MacPorts**

    Here are the exact steps I just verified worked. Note that I *first installed the Haskell Platform*, described further down this page; that installed some developer tools that were needed to build and install Chicken. If you don't know how to open a Terminal, move between directories, copy / rename / delete files and so on, then you're probably best off not doing this. You could break something.

    1. Go to <http://code.call-cc.org>, and click the "Source code" link near the top. Current version is 4.9.0.1, released November 2014. This should fetch a file to your download folder, and will probably automatically unpack that file into a folder, "chicken-4.9.0.1". Click on that folder and press command-C / Copy, then open a Terminal.
    2. In the terminal type `cd` followed by a space, then press command-V / Paste. Then press enter. This will move your session into the folder you just downloaded.  <!-- Type `less README` and read that file. -->
    3. Type `make PLATFORM=macosx XCODE_DEVELOPER= XCODE_TOOL_PATH=/usr/bin PREFIX=$HOME` <!-- PREFIX defaults to /usr/local -->

    The options starting with `XCODE_` are to tell the Chicken build scripts that I've got the developer tools installed in my main system, rather than as part of Xcode. (That's where the Haskell Platform installer put them.) Continuing:

    4. Wait a while while Chicken builds.
    5. If it finishes with no errors, then type `make PLATFORM=macosx XCODE_TOOL_PATH=/usr/bin PREFIX=$HOME install`. This will install Chicken in your user home directory.
    6. At this point you can type `which chicken`. It should give you an answer of "/Users/yourname/bin/chicken".
    7. In your terminal, type `chicken-install r7rs datatype matchable monad`. <!-- with "-sudo" if you installed chicken in /usr/local --> This will download, build, and install a few extensions (Chicken calls them "eggs") relevant to ideas we'll be working with in this course.

*   **To install on Mac with MacPorts**

    Unfortunately, MacPorts doesn't have Racket itself available. It only has an older version from when they still called
    themselves PLT Scheme. And even then, it only has the command-line program "mzscheme" (what's nowadays called "racket"); it
    doesn't have the GUI program that corresponds to what's now called "DrRacket". You can install mzscheme by opening a Terminal
    window and typing:

         sudo port install mzscheme

    <!-- mzscheme v4.1.5, from March 2009; latest mzscheme is 4.2.5, from April 2010 -->

    If you want the GUI components, I think you'll need to use the
    "Mac/without MacPorts" installation options above. Or you could try the Chicken Scheme implementation instead of Racket. This is more current.
    To do that, type:

        sudo port install chicken readline

    <!-- chicken v4.8.0.2, from Feb 2013; latest available is 4.9.0.1, from Nov 2014 -->

    Whether you use mzscheme or Chicken, I recommend also typing:

        sudo port install rlwrap

    then if you ever use the command-line program `mzscheme` (or `racket`, for that matter), you should start it by typing `rlwrap mzscheme` (or whatever). This gives
    you a nice history of the commands you've already typed, which you can scroll up and down in with your
    keyboard arrows.

*   **To install on Linux**

    Use your packaging system, for example, open a Terminal and
    type:

         sudo apt-get install racket

    It's very likely that your packaging system has some version of
    Racket available, so look for it. However, if you can't find it you
    can also install a pre-packaged binary from the Racket website at <http://racket-lang.org/download/>.
    Choose the option for your version of Linux (Ubuntu and Debian are available).

    As above, I recommend you also type:

        sudo apt-get rlwrap

    then if you ever use the command-line program `mzscheme` (or `racket`), you should start it by typing `rlwrap mzscheme` (or whatever). This gives
    you a nice history of the commands you've already typed, which you can scroll up and down in with your
    keyboard arrows.


<a name=ocaml></a>
## Getting OCaml ##

**Caml** is one of two major dialects of *ML*, which is another large family of
programming languages. The other dialect is called "SML" and has several
implementations. But Caml has only one active implementation, OCaml or
Objective Caml, developed by the INRIA academic group in France.
Sometimes we may refer to Caml or ML
more generally; but you can assume that what we're talking about always works more
specifically in OCaml.

It's helpful if in addition to OCaml you also install the
Findlib add-on and/or the [OPAM](https://opam.ocaml.org) "package manager."
These will make it easier to install additional add-ons further down the road.
However, if you're not able to get them working, don't worry about it much.

The current version of OCaml is 4.02.1 (released October 2014).
<!-- 3.12.1 July 2011; 4.00.1 Oct 2012; 4.01.0 Sept 2013; 4.02.0 Aug 2014; 4.02.1 Oct 2014 -->


*   In your web browser:

    There is a (slow, bare-bones) version of OCaml available for online use at <http://try.ocamlpro.com/>.


*   **To install in Windows**

    There are *five* different strategies for installing OCaml on Windows. I don't know which works best.

    1.  First, you can go to <http://caml.inria.fr/download.en.html>.
    You can probably download and install the
    "Self installer for the port based on the MinGW toolchain"
    even if you don't know what MinGW or Cygwin are.
    Some features of this require Cygwin, but it looks like
    it should mostly work even for users without Cygwin.
    At the time of this writing, only an installer for an earlier
    version of OCaml (4.01.0, from September 2013) is available.

    2.  A second strategy uses a package called
        [OCPWIN](http://ocaml.org/docs/install.html#OCPWINSelfContainedOCamlforWindows). This also installs only version 4.01.0.

    3.  The [three remaining strategies](http://ocaml.org/docs/install.html#OCamlonCygwin) in some way
    use the Cygwin environment, mentioned earlier on this page. At least one of
    those three methods will automatically fetch and help you install Cygwin.
    The first method listed on that page says it installs version 4.00.1, but
    really it's been updated and now installs the (somewhat newer, but still
    not the newest) version 4.01.0.

    Some of these methods may automatically install Findlib for you. If not,
    you can try installing it yourself but I think you'll need the Cygwin
    system installed to do so. I'm not going to explain how to do this.
    If you want to figure it out yourself, go to the
    Findlib website at <http://projects.camlcity.org/projects/findlib.html>.

*   **To install on Mac without MacPorts**

    The people in charge of OCaml (they're at the French research institute INRIA) have stopped making pre-built packages for Mac OS X. One option you have is to use their package for a slightly older version of OCaml, 4.01.1 from Sept. 2013. You can find that as a "Precompiled binary for Mac OS X" on [this page](http://ocaml.org/releases/4.01.0.html). If, when you attempt to install this package, you get an error about its being from an "unidentified developer," you need to control-click on the `ocaml.pkg` file and select "Open", then when the warning box appears again, this time there will be an "Open" button that you can click. Then you can continue running the Installer.

    A second option is to install the OPAM package manager and use that to build and install the latest version of OCaml. Here's how to do that:

    1.  Download [this file](https://raw.github.com/ocaml/opam/master/shell/opam_installer.sh) and
    note where it gets saved to. If it opens in your browser, then type
    command-S / Save Page and save it somewhere on your disk, again noting its
    location.

    2.  Open a terminal and type:

            sh /path/to/opam_installer.sh ~/bin

        Except replace `/path/to` with the real location, that you noted in step 1. When prompted "Do you want OPAM to modify ~/.bash_profile and ~/.ocamlinit?", say "y".

    3.  If that works, then type:

            opam init --comp 4.01.0

        or whatever it was that the OPAM installer prompted you to type. This will download and install a fresh version of OCaml, and will take a bit of time.

<!-- To upgrade: opam switch 4.02.1 && eval `opam config env` -->

<!--
If you do have Xcode, and want to do without MacPorts, then
what you need to do is download Findlib from
<http://download.camlcity.org/download/findlib-1.2.6.tar.gz>.
Unpack the download, open a Terminal and go into the folder you just
unpacked, and type:

    ./configure
    make package-macosx

This will build an installer package which you should be able to
double-click and install.
-->

*   **To install on Mac with MacPorts**

    You can install the current version of OCaml (4.02.1, from October 2014),
    together with the Findlib add-on and OPAM package manager, by opening a Terminal and typing:

        sudo port install ocaml ocaml-findlib opam

    As with Scheme, it's helpful to also have rlwrap installed, and to start OCaml as `rlwrap ocaml`. This gives
    you a nice history of the commands you've already typed, which you can scroll up and down in with your
    keyboard arrows.

*   **To install on Linux**

    Use your packaging system, for example, open a Terminal and
    type:

        sudo apt-get install ocaml opam camlp4-extra ocaml-findlib

    That will install a version of OCaml and the Findlib add-on and OPAM package manager.

    If you're using Ubuntu "Utopic" (14.10), there's [a note on the OPAM home page](https://opam.ocaml.org/doc/Install.html)
    warning that its version of OPAM is broken, and not to use it. Here's how you can get (OCaml and) OPAM from a newer repository:

        sudo apt-get install -y software-properties-common
        sudo add-apt-repository -y ppa:avsm/ppa
        sudo apt-get update
        sudo apt-get install ocaml opam

    If for some reason you can't get OCaml through your Linux packaging system, you can go to
    <http://caml.inria.fr/download.en.html>.
    Pre-packaged binary installers are available for several Linux systems.

    If you can't get findlib through your packaging system, you'll need to download it from
    <http://download.camlcity.org/download/findlib-1.5.5.tar.gz>.
    and use gcc to compile it yourself. If you don't know how to do that, you probably don't want to attempt this.
    Here are the INSTALL notes:
    <https://godirepo.camlcity.org/svn/lib-findlib/trunk/INSTALL>.

    As with Scheme, it's helpful to also have rlwrap installed, and to start OCaml as `rlwrap ocaml`. This gives
    you a nice history of the commands you've already typed, which you can scroll up and down in with your
    keyboard arrows.


<!-- More info on installing Ocaml and VMs at <http://ocaml.org/learn/teaching-ocaml.html#OCamlinstallation> -->


<a name=haskell></a>
## Getting Haskell ##

This last installation is less crucial than the others, since we will be focusing
primarily on Scheme and OCaml. However we, and the readings you come across,
will sometimes mention Haskell, so it might be worth your installing this too,
so that you have it available to play around with.

Haskell is used a lot in the academic contexts we'll be working through. At one point, Scheme
dominated these discussions but now Haskell seems to do that.

Haskell's surface syntax differs from Caml, and there are various important things one can do in
each of Haskell and Caml that one can't (or can't as easily) do in the
other. But these languages also have *a lot* in common, and if you're
familiar with one of them, it's generally not hard to move between it and the
other.

*   In your web browser:

    There is a (slow, bare-bones) version of Haskell available for online use at <http://tryhaskell.org/>.

Like Scheme, Haskell has a couple of different implementations. The dominant one, and the one we recommend you install, is called [GHC](https://wiki.haskell.org/GHC), short for "Glasgow Haskell Compiler". To install this on your machine, there are a couple of different strategies. It's helpful to understand some lingo as you begin this process:

*   As mentioned, **GHC** is the main Haskell engine or compiler you'll be installing. The current version is 7.8.4, from December 2014.
*   **gcc** and **llvm/clang** and **Xcode** and **MinGW** are names for other compilers on various systems. Oftentimes these will be used during the installation process to get GHC up and running. Some of the strategies described below will help you install these if they're not already on your machine.
*   **alex** and **happy** and **haddock** are names of various Haskell helper programs that GHC uses to get up and running.
*   **cabal** is a "package manager" for Haskell. It allows you to install libraries or extensions that other people have built. (Usually those are published at the [Hackage](https://hackage.haskell.org) Package Database.) Some of these are experimental and may not always work; others are quite fundamental and are almost de facto parts of what people expect in a Haskell system.
*   The **[Haskell Platform](https://www.haskell.org/platform/contents.html)** is a standard bundle that includes a specific version of GHC, plus specific versions of some of the most popular libraries or extensions. This is updated once or twice a year. The current version is 2014.2.0.0, from August 2014. It includes GHC version 7.8.3.

The easiest way to get up and running with Haskell/GHC is to install the Haskell Platform. Here's how to do that **on Windows**:

*   Go to <https://www.haskell.org/platform/windows.html> and follow the instructions. It looks like this process will automatically install the MinGW compiler needed to get this build of Haskell running on Windows.

On **Mac without MacPorts**:

*   Go to <https://www.haskell.org/platform/mac.html> and follow the instructions. This requires Mac OS X 10.6 / Snow Leopard or later; but there is a link to an earlier version of the Haskell Platform, that's built for Mac OS X 10.5 / Leopard. During the installation, you may be prompted to install "the command line developer tools"; this is a portion of what Apple bundles together with Xcode (mentioned above on this page). The installer will take care of getting these for you if you give it permission.

<!--
The Installer places everything in your system directories. If you'd like it instead in your user directory (easier to clean up later), you can do this after running the Installer:

    mkdir ~/Library/Frameworks
    cp -a /Library/Frameworks/GHC.framework ~/Library/Frameworks/
    [ -d ~/Library/Haskell ] && mv ~/Library/Haskell ~/Library/Haskell.orig
    sudo mv /Library/Haskell ~/Library/
    sudo chown -Rh $USER:staff ~/Library/Haskell
    mkdir -p ~/share/doc ~/share/man/man1
    ln -s ~/Library/Frameworks/GHC.framework/Versions/Current/usr/share/doc/ghc ~/share/doc/
    ln -s ~/Library/Frameworks/GHC.framework/Versions/Current/usr/share/man/man1/ghc.1 ~/share/man/man1/
    sudo rm -r /usr/share/doc/ghc /usr/share/man/man1/ghc.1 /Library/Frameworks/GHC.framework
    for f in ghc ghc-7.8.3 ghc-pkg ghc-pkg-7.8.3 ghci ghci-7.8.3 haddock haddock-ghc-7.8.3 hp2ps hpc hsc2hs runghc runghc-7.8.3 runhaskell; do
      ln -s ~/Library/Frameworks/GHC.framework/Versions/7.8.3-*/usr/bin/$f ~/bin/
      sudo rm /usr/bin/$f
    done
    for f in activate-hs alex cabal cabal.real cabal.wrap ghc-clang-wrapper happy HsColour uninstall-hs; do
      ln -s /Library/Haskell/ghc-7.8.3-*/bin/$f ~/bin/
      sudo rm /usr/bin/$f
    done
    sed -i "" "s=/Library=$HOME/Library=g" $(fgrep -RIl /Library ~/Library/Haskell ~/Library/Frameworks/GHC.framework | fgrep -v .html)

# Ehh. Doesn't work...
-->

On **Mac with MacPorts**:

*   In a Terminal, type `sudo port install haskell-platform`.

On **Ubuntu or Debian Linux**:

*   In a Terminal, type `sudo apt-get install haskell-platform`.


If any of the instructions above don't work, then you can try alternative instructions for [Mac](http://new-www.haskell.org/downloads/osx) or [Windows](http://new-www.haskell.org/downloads/windows) or [Ubuntu](http://new-www.haskell.org/downloads/linux). Note that this method doesn't install all the extensions that are part of the Haskell Platform, but only the core pieces of GHC. You can use Cabal to download and manage any extra extensions you turn out to need, down the road.

**After installing Haskell**, open a Terminal and type:

    cabal update

It may give you a message about updating your `PATH` variable. On my Mac, I was prompted to do this:

    echo 'export PATH="$HOME/Library/Haskell/bin:$PATH"' >> ~/.bash_profile

On a Linux machine, or if you installed Haskell differently on your Mac, you might have to type instead:

    echo 'export PATH="$HOME/.cabal/bin:$PATH"' >> ~/.bash_profile

Some instructions may say to use `.bashrc` instead of `.bash_profile`. These files do similar jobs.

After issuing the relevant `echo` command, I exited the Terminal and started a new Terminal session. Now if I type `echo $PATH` I should see the directory I just added in the list. Now I can contine setting up Cabal. I type:

    which alex happy

If that gives me back two pathnames, one to the program `alex` and the other to the program `happy`, then I'm already finished. If not, then I type:

    cabal install alex happy

This installs those two programs. They are helpers that Cabal needs to build and install some packages.

<!-- https://github.com/pittsburgh-haskell/haskell-installation -->