[PL-sem-jr] Monad exercises

[Hugo Musso Gualandi]

Based on feedback from people who already tried the exercises, here are
some tips:

- The second problem (error handling) is easier than the first one
(counting operations). I'd do them in that order.

- The do-notation exercises really are a bit awkward because of the
applicative and functor stuff. They are probably not worth the hassle
unless you already know Haskell very well.

- As is usually the case with Haskell, it is often easier to think in
terms of types when writing the code. If it the typechecker accepts it,
it is probably correct.

- If you are getting stuck because of the Haskell syntax, feel free to
use a different language instead. The only Haskell features the first
two exercises need are alebraic data types and first class functions.
(Type classes are only needed for do-notation)

Have fun!

-- Hugo

On Wed, 2018-11-21 at 21:27 -0500, Artem Pelenitsyn wrote:
> Hi, here is the three files loaded into online IDE. Click FORK in the
> upper left corner to start editing your version.
> 
> 1) m01_direct.hs https://ideone.com/lyQPo8
> 2) m02_monadic.hs https://ideone.com/iw3CWI
> 3) m03_donotation.hs https://ideone.com/NDUwy6
> 
> (I only had to rename modules to Main and add main function to make
> online thing happy)
> 
> -- Best, Artem
> 
> On Wed, 21 Nov 2018 at 18:31 Hugo Musso Gualandi <
> hgualandi at inf.puc-rio.br> wrote:
> > Hi everyone,
> > 
> > I prepared two exercises for playing with Monads, highlighting the
> > State and the Maybe monads. I lifted them from the Wadler paper
> > that
> > we floated around earlier.
> > 
> > The files can be downloaded from my website (my previous attempt to
> > attach them to this email hit a paranoid the antivirus filter):
> > 
http://www.inf.puc-rio.br/~hgualandi/stuff/pljr-monad-problems.tar.gz
> > 
> > The task for the exercizes is to fill in the "undefined" blanks in
> > the
> > example files I provided and to get the code to work. There are
> > three
> > files:
> > 
> > m01_direct: Try to implement the functions with straightforward
> > Haskell
> > code.
> > 
> > m02_monadic: This time, implement the monadic "bind" and "return"
> > functions and reimplement the evaluators using them.
> > 
> > m03_donotation: This one adds the necessary boilerplate to the code
> > from the previous exercise, so it can be hooked up with the actual
> > Monad typeclass and so you can use do-notation with it. I found
> > that it
> > got a bit clunky, so I consider it "extra credit".
> > 
> > I tried to keep these short but please let me know if you need
> > anything
> > else.
> > 
> > -- Hugo
> > 
> > 
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