4 ms·

I have heard similar opinions on Haskell. I am definitely attracted to the convenient function currying and composition, but I realized I could do similar in C

by Xurinos 16y ago

I have heard similar opinions on Haskell. I am definitely attracted to the convenient function currying and composition, but I realized I could do similar in CL and make it look like whatever made sense to me. I find the ability to create my own look and feel to supercede accepting someone else's look and feel. I have no issues with Scheme, except that I have chosen to use CL over Scheme because it does feel like something of a batteries-included system. On the other hand, I was annoyed by what I felt was inconsistent syntax with Haskell revealed in Real World Haskell chapter 13 (unfortunately my only experience with it) when they showed this function definition: mkFuncRec :: String -> (Int -> Int) -> FuncRec vs this function definition: simplify :: (Num a) => SymbolicManip a -> SymbolicManip a The =>, previously used to instance types, confused me here (they never explained how this definition differed), and I was having a hard time keeping up with all the various times I needed to use each special symbol. Of course, I tolerated it through C++ and perl, so if I ever decided to try a project, I could probably get used to it.

eru 16y ago
I see that the namespaces for values and types are somewhat separate in Haskell. Could you please describe your confusion again in different words? Perhaps I am too used to Haskell, but I do not see anything confusing in those two definitions. What do you mean with "previously used to instance types"? As far as I can remember => is only ever used in the context shown above.
- Xurinos 16y ago
  The book introduced the second pattern out of the blue. What is the difference between those two function definitions? What does "=>" mean in this context? a :: b -> (c d) -> e makes sense to me, but f :: (g h) => i -> j -> k does not. Here is the page that suddenly introduced that second form: http://book.realworldhaskell.org/read/data-structures.html http://book.realworldhaskell.org/read/data-structures.html It is entirely possible I missed some context somewhere in there; "namespaces for values vs types" might be my clue. :)
  - eru 16y ago
    In the example my_fun :: (TypeClass1 a, Typeclass2 b) => a -> b the stuff preceeding the => declares what typeclasses the types you mention later should fall into. A good example is the module Data.Map; this module deals with finite mappings of keys to values. Since those Maps are based on balanced trees, the keys have to be orderable/comparable. So for inserting a key into a map (http://hackage.haskell.org/packages/archive/containers/0.2.0.1/doc/html/Data-Map.html#5 http://hackage.haskell.org/packages/archive/containers/0.2.0...) we get the following type insert :: Ord k => k -> a -> Map k a -> Map k a This just says that the type of keys has to be an instance of the class Ord (http://haskell.org/ghc/docs/6.12.1/html/libraries/base-4.2.0.0/Data-Ord.html http://haskell.org/ghc/docs/6.12.1/html/libraries/base-4.2.0...). I.e. there has to be an instance declaration with the function (<=) :: a -> a -> Bool Does that help? By the way, if you want to find documentation about a function and you know its name or type, you can use Hoogle (http://www.haskell.org/hoogle/ http://www.haskell.org/hoogle/).
    - Xurinos 16y ago
      the stuff preceeding the => declares what typeclasses the types you mention later should fall into. That makes it clear. Thank you!

by Xurinos 16y ago

eru 16y ago

I see that the namespaces for values and types are somewhat separate in Haskell. Could you please describe your confusion again in different words? Perhaps I am too used to Haskell, but I do not see anything confusing in those two definitions. What do you mean with "previously used to instance types"? As far as I can remember => is only ever used in the context shown above.

Xurinos 16y ago
The book introduced the second pattern out of the blue. What is the difference between those two function definitions? What does "=>" mean in this context? a :: b -> (c d) -> e makes sense to me, but f :: (g h) => i -> j -> k does not. Here is the page that suddenly introduced that second form: http://book.realworldhaskell.org/read/data-structures.html http://book.realworldhaskell.org/read/data-structures.html It is entirely possible I missed some context somewhere in there; "namespaces for values vs types" might be my clue. :)
- eru 16y ago
  In the example my_fun :: (TypeClass1 a, Typeclass2 b) => a -> b the stuff preceeding the => declares what typeclasses the types you mention later should fall into. A good example is the module Data.Map; this module deals with finite mappings of keys to values. Since those Maps are based on balanced trees, the keys have to be orderable/comparable. So for inserting a key into a map (http://hackage.haskell.org/packages/archive/containers/0.2.0.1/doc/html/Data-Map.html#5 http://hackage.haskell.org/packages/archive/containers/0.2.0...) we get the following type insert :: Ord k => k -> a -> Map k a -> Map k a This just says that the type of keys has to be an instance of the class Ord (http://haskell.org/ghc/docs/6.12.1/html/libraries/base-4.2.0.0/Data-Ord.html http://haskell.org/ghc/docs/6.12.1/html/libraries/base-4.2.0...). I.e. there has to be an instance declaration with the function (<=) :: a -> a -> Bool Does that help? By the way, if you want to find documentation about a function and you know its name or type, you can use Hoogle (http://www.haskell.org/hoogle/ http://www.haskell.org/hoogle/).
  - Xurinos 16y ago
    the stuff preceeding the => declares what typeclasses the types you mention later should fall into. That makes it clear. Thank you!