lyah | learn you a haskell for great good 中文版 | Functional Programming library

I just started on Haskell and really love the language! Was looking for some installation help.

I just finished CIS194 and most of the excellent LYAH book. I am currently doing the fp-course recommended here: https://github.com/bitemyapp/fp-course

My issue is that i've done of my work on a mac os laptop up to this point, and now want to do a haskell installation on my windows desktop to work on my larger and more comfortable home setup; however i've struggled to find a method to do a "clean" installation. The haskell platform keeps recommending choclatey which doesn't seem to offer me a choice to change the download location. My issue is that i use a small SSD for my OS drive, and have a large 2TB secondary drive where i would like the installation to go instead.

My other point of confusion is that some people seem to vehemently recommend a stack installation instead of the haskell platform installation; whilst others say it doesn't matter. I'm a beginner so I doubt it matters to me but the haskell platform and choclatey were extremely frustrating as after I installed them, not only was I not able to find a beginner friendly way to change the installation directory, deleting packages/haskell entirely was extremely obtuse and hard to find resources for.

My concern is that over time, this will take a significant amount of space on my smaller system drive, forcing me to reformat again. I'm not sure if a Stack installation will be any better in this regard but I'm hoping for an installation that lets me choose exactly where all the files go.

Many posts outlined an uninstaller that should have come with the haskell platform, but it did not for me and was not shown in my add or remove programs so i had to resort to simply reformatting and am now looking for help before jumping back in (to hopefully avoid doing this again).

In summary, could I have help with doing an installation on a non-home drive, that is very easily removed, with clear knowledge of exactly where all the haskell files are, on a Windows 10 machine? Would really appreciate any help with this!

I'm trying to implement a function that adds an element (a type) to a list of this type to an existing created datatype. Since Haskell data variable are immutable, I know that you have to create a new data with the same characteristic as the first one and add onto it, but I can seem to make ghci compile my program and make it do what I'm trying to accomplish.

Here is my code and the function which should add a contact to a list of already existing contact addContact which I'm been trying to work on:

I have created the type Contact, and I'm trying to create a function that takes 4 parameters (First Name, Last Name, Phone and State) and creates a contact and adds it to a list of existing contact.

Question is in bold at the bottom.

LYAH gives this example of using the do notation with the Writer monad

Functional Programming in C++, at page 214, with reference to an expected monad which is the same as Haskell's Either, reads

[...] as soon as any of the functions you're binding to returns an error, the execution will stop and return that error to the caller.

Then, in a caption just below, it reads

If you call mbind [equivalent to Haskell's >>=] on an expected that contains an error,, mbind won't even invoke the transformation function; it will just forward that error to the result.

which seems to "adjust" what was written earlier. (I'm pretty sure that either LYAH or RWH underlines somewhere that there's no short-circuiting; if you remember where, please, remind me about it.)

Indeed, my understanding, from Haskell, is that in a chain of monadic bindings, all of the bindings happen for real; then what they do with the function passed to them as a second argument, is up to the specific monad.

In the case of Maybe and Either, when the bindings are passed a Nothing or Left x argument, then the second argument is ignored.

Still, in this specific two cases, I wonder if there's a performance penalty in doing something like this

I'm relatively new to Haskell, and have been trying to learn it for the past few weeks, but have been stuck on Filters and Predicates, which I was hoping to get help with understanding.

I have come across a problem whereby I have a list of tuples. Each tuple consists of a (songName, songArtist, saleQty) and am required to remove a tuple from that list based on the user inputting the songName and SongArtist.

When returning the results, I understand I can remove a tuple by using the Filter function when returning the results. I have been doing some reading on it using LYAH. Its taught me that I have to use a Predicate (which is another function) to filter through my results. This has caught me off guard as I learnt a Filter function has type (a -> Bool) -> [a] -> [a], which means my input for the Filter needs to to be a Boolean and my output for my Predicate needs to be Boolean so it can be fed to the Filter.

This is a problem, as to filter my results from the list I need to input the songName and songArtist (both of which are String types) to the predicate when recursively going through the results, and output the songName and songArtist to the Filter to let it know which exact tuple needs to be removed from the list.

Am I going about this the wrong way or is there a better way I could go about this?

From LYAH I understand that the do notation is just syntactic sugar for monadic style; and from the wikibook I read more or less the same; so my understanding is that there can't be any do notation if there's no Monad instance.

Yet I read this definition of the Functor instance of the IO type ctor.