I took a trip to Haskell.org to investigate your question What I found are two important papers you ought to read to further your research, and I am building my answer to your question from these scholarly papers. Push-Pull FRP by Conal Elliott Generalising Monads to Arrows by John Hughes Yes, but also no. According … Read more
One reason for avoiding Template Haskell is that it as a whole isn’t type-safe, at all, thus going against much of “the spirit of Haskell.” Here are some examples of this: You have no control over what kind of Haskell AST a piece of TH code will generate, beyond where it will appear; you can … Read more
It’s a strictness declaration. Basically, it means that it must be evaluated to what’s called “weak head normal form” when the data structure value is created. Let’s look at an example, so that we can see just what this means: data Foo = Foo Int Int !Int !(Maybe Int) f = Foo (2+2) (3+3) (4+4) … Read more
Disclaimer: A lot of this doesn’t really work quite right when you account for ⊥, so I’m going to blatantly disregard that for the sake of simplicity. A few initial points: Note that “union” is probably not the best term for A+B here–that’s specifically a disjoint union of the two types, because the two sides … Read more
I’ll try to give an explanation in simple terms. As others have pointed out, head normal form does not apply to Haskell, so I will not consider it here. Normal form An expression in normal form is fully evaluated, and no sub-expression could be evaluated any further (i.e. it contains no un-evaluated thunks). These expressions … Read more
First of all, your function has the wrong type; I am pretty sure it should be (without the context) a -> (a -> b) -> b. GHC 7.10 is somewhat more helpful in pointing that out, because with your original code, it complains about a missing constraint Internal (a -> b) ~ (Internal a -> … Read more
What I recommend. Read code by people from different grad schools in the 1990s Oxford style Glasgow style or (this) Chalmers style (or this) York style Portland style or OGI style (or this) Utrecht style Yale style Special case: CMU/Elliott Read code by the old masters certain people (incomplete list) Marlow; Paterson; Peyton Jones; Gill; … Read more
Let’s start with a code example: foob :: forall a b. (b -> b) -> b -> (a -> b) -> Maybe a -> b foob postProcess onNothin onJust mval = postProcess val where val :: b val = maybe onNothin onJust mval This code doesn’t compile (syntax error) in plain Haskell 98. It requires … Read more
Short answers: The question’s key points, as I understand them, are the following: “is the auto-specialization transitive?” Should I only expect (+) to be specialized transitively with an explicit pragma? (apparently intended) Is this a bug of GHC? Is it inconsistent with the documentation? AFAIK, the answers are No, mostly yes but there are other … Read more
Why do we need monads? We want to program only using functions. (“functional programming (FP)” after all). Then, we have a first big problem. This is a program: f(x) = 2 * x g(x,y) = x / y How can we say what is to be executed first? How can we form an ordered sequence … Read more