stephendiehl.com | Stephen Diehl 's Blog & Website | Learning library

I've been reading the book "What I wish I knew when learning Haskell" and I stopped on this example:

I am trying to rename keys when serializing an object to json.

I understand the way to do that is to, rather than just using deriving generic, define an instance with custom key names like so:

In order to have a better understanding of packrat I've tried to have a look at the provided implementation coming with the paper (I'm focusing on the bind):

I'm having trouble understanding how the following code works. I'm trying to follow the parser example found here. I have used ReadP before and want to get a more in-depth understanding of how parsers work. My question isn't specific to parsers, rather to how function application in Haskell works. Here's the code:

In prelude, head has the following signature : head :: [a] -> a which makes it unsafe on empty list, which is not good !! (head :: [a] -> Maybe a is the good way :-) )

this applies for a couple of other functions on list : last, tail, init minimum, maximum, cycle, last, init, foldl1, cycle... there are actually a lot of these calling errorEmptyList

Quoting Stephen Diehl from his website :

"Safe provides Maybe versions of many of the various partial functions (head, tail) that are shipped by default. Wrapping it up in a Maybe is widely considered the right approach and if Haskell were designed today, they would not be present."

I would love to see these unsafe functions tagged somehow with some convention at least because I don't think any of us like when an exception blows up in production :-)

What prevents the community from fixing these issues in the prelude ?

From the Haddock section on Stephen Diehl's "What I Wish I Knew When Learning Haskell" page:

haddock options can also be specified with pragmas in the source, either at the module or project level.

An example of a pragma at the module level is given:

{-# OPTIONS_HADDOCK show-extensions, ignore-exports #-}

but in which section of which file (when using stack) can these options be placed so as to apply to an entire project (or rather, "package")?

I am following this tutorial for implementing Parser Combinators (a la parsec) in Haskell. I implemented everything of the NanoParsec mentioned throught this post.

For some hours now, I am struggeling to implement