opam switch 4.02.0+improved-errors && opam install --switch=4.02.0+improved-errors delimcc && eval `opam config env`
- Installing the `delimcc` library gives you [Oleg's Delimited Continuation library for OCaml](http://okmij.org/ftp/continuations/implementations.html), which we will encourage you to play around with later in the term. It's not essential to have it, though. There are some advantages to using one of the 4.02.x versions of OCaml, though, rather than the 4.01.0 version I think most of us ended up installing. One advantage is that now you can use the special <code>#show <i>symbol</i></code> command in OCaml sessions, which works like Haskell's special <code>:info <i>symbol</i></code> inside a GHCi session. Then for example, instead of having to type:
+ Installing the `delimcc` library gives you [Oleg's Delimited Continuation library for OCaml](http://okmij.org/ftp/continuations/implementations.html), which we will encourage you to play around with later in the term. <!-- see also http://stackoverflow.com/questions/14431257 --> It's not essential to have it, though. There are some advantages to using one of the 4.02.x versions of OCaml, though, rather than the 4.01.0 version I think most of us ended up installing. One advantage is that now you can use the special <code>#show <i>symbol</i></code> command in OCaml sessions, which works like Haskell's special <code>:info <i>symbol</i></code> inside a GHCi session. Then for example, instead of having to type:
module type SOMETHING = Monad.OPTION
#show Monad.OPTION
-2. The program that starts up when you type `ocaml` is OCaml's Standard "Toplevel" Interactive Interpreter. There's an alternative interactive interpreter that you can try out, which some people like. It's called **utop** and [you can read about it here](https://github.com/diml/utop) or [here](https://opam.ocaml.org/blog/about-utop). To install it, you can just type `opam install utop`. I'm not so crazy about it myself. But I prefer to use *some* kind of helper program with OCaml's Standard Toplevel, because the Standard Toplevel itself doesn't let you scroll back through commands you typed previously, has only very rudimentary facilities for editing a line if you made a mistake and so on. One virtue of utop is that it does those things better, but there are also other ways to do them better. What I use is a wrapper program called **rlwrap**. Here are instructions for how to install that:
+2. The program that starts up when you type `ocaml` is OCaml's Standard "[[Toplevel|/topics/week8_monads_and_modules/#toplevel]]" Interactive Interpreter. There's an alternative interactive interpreter that you can try out, which some people like. It's called **utop** and [you can read about it here](https://github.com/diml/utop) or [here](https://opam.ocaml.org/blog/about-utop). To install it, you can just type `opam install utop`. I'm not so crazy about it myself. But I prefer to use *some* kind of helper program with OCaml's Standard Toplevel, because the Standard Toplevel itself doesn't let you scroll back through commands you typed previously, has only very rudimentary facilities for editing a line if you made a mistake and so on. One virtue of utop is that it does those things better, but there are also other ways to do them better. What I use is a wrapper program called **rlwrap**. Here are instructions for how to install that:
> First, I had to upgrade the version of the "GNU readline" library on my computer. My Mac with System 10.9.5 has a version of that library, but it's too old to use with recent versions of `rlwrap`. So I downloaded [the source code for GNU readline](http://ftp.gnu.org/gnu/readline/readline-6.3.tar.gz). Double click the downloaded archive to expand it, if your browser doesn't do that automatically. Then go inside the `readline-6.3` folder in a Terminal. On a Mac, you can click on the folder in the Finder and do a Copy (or cmd-C). Then open a Terminal and type `cd` followed by a space then do a Paste (cmd-V). Then press <code><i>return</i></code>. Once you're inside the `readline-6.3` folder, type this command in the Terminal: