There remains a final major Monad, the Continuation monad, that we'll discuss and add to the library later.
-We'll discuss the different `ask, shift, pick`, and so on functions [[on another page|/topics/week9_using_the_monad_library/]]. But just to give some examples, in the List monad, `mzero` corresponds to `[]` and `++` as we mentioned before corresponds to `List.append`, which OCaml also writes as the infix operator `@`. For some reason I don't like that operator, so I mostly avoid it. Maybe I don't like it because Haskell uses it with a different meaning. In Haskell, <code><i>var</i> @ <i>pat</i></code> is what OCaml writes as <code><i>pat</i> as <i>var</i></code>. (Discussed in Rosetta1. TODO LINK) So I tend to write instead just `List.append`. But when working with Lists as abstract monadic values, in OCaml, you need to use `++` instead of `List.append`. OCaml will act like it doesn't know that abstract monadic Lists are really `list`s. `test` takes a predicate of plain (non-monadic) lists, and if the monadic list that is its second argument satisfies it, returns that list unchanged, else returns `mzero` (the abstract list version of `[]`). `guard` takes a boolean argument, and if it's true returns `[()]` (as an abstract list) else returns `mzero`. These correspond to the Haskell operations of the same name.
+We'll discuss the different `ask, shift, pick`, and so on functions [[on another page|/topics/week9_using_the_monad_library/]]. But just to give some examples, in the List monad, `mzero` corresponds to `[]` and `++` as we mentioned before corresponds to `List.append`, which OCaml also writes as the infix operator `@`. For some reason I don't like that operator, so I mostly avoid it. Maybe I don't like it because Haskell uses it with a different meaning. In Haskell, <code><i>var</i> @ <i>pat</i></code> is what OCaml writes as <code><i>pat</i> as <i>var</i></code>. (Discussed on our [[Rosetta1 page|/topics/week1_kapulet_advanced/#as-patterns]]) So I tend to write instead just `List.append`. But when working with Lists as abstract monadic values, in OCaml, you need to use `++` instead of `List.append`. OCaml will act like it doesn't know that abstract monadic Lists are really `list`s. `test` takes a predicate of plain (non-monadic) lists, and if the monadic list that is its second argument satisfies it, returns that list unchanged, else returns `mzero` (the abstract list version of `[]`). `guard` takes a boolean argument, and if it's true returns `[()]` (as an abstract list) else returns `mzero`. These correspond to the Haskell operations of the same name.
Here is an example of using the List monad.