We will however try to give some general advice about how to translate between OCaml and Haskell.
* Again, it may sometimes be useful to [try Haskell in your web browser](http://tryhaskell.org/)
-* There are many Haskell tutorials and textbooks available. This is probably the most actively developed: [Haskell Wikibook](http://en.wikibooks.org/wiki/Haskell)
-* [Yet Another Haskell Tutorial](http://www.cs.utah.edu/~hal/docs/daume02yaht.pdf) (much of this excellent book has supposedly been integrated into the Haskell Wikibook)
-* All About Monads has supposedly also been integrated into the Haskell Wikibook
+* There are many Haskell tutorials and textbooks available. This is probably the most actively developed: [Haskell wikibook](http://en.wikibooks.org/wiki/Haskell)
+* [Yet Another Haskell Tutorial](http://www.cs.utah.edu/~hal/docs/daume02yaht.pdf) (much of this excellent book has supposedly been integrated into the Haskell wikibook)
+* All About Monads has supposedly also been integrated into the Haskell wikibook
* (A not-so-)[Gentle Introduction to Haskell](http://web.archive.org/web/http://www.haskell.org/tutorial/) (archived)
* [Learn You a Haskell for Great Good](http://learnyouahaskell.com/)
type Weight = Integer
type Person = (Name, Address) -- supposing types Name and Address to be declared elsewhere
- then you can use a value of type `Integer` wherever a `Weight` is expected, and vice versa. `newtype` and `data` on the other hand, create genuinely new types. `newtype` is basically just an efficient version of `data` that you can use in special circumstances. `newtype` must always take one type argument and have one value constructor. For example:
+ then you can use a value of type `Integer` wherever a `Weight` is expected, and vice versa. <!-- `type` is allowed to be parameterized -->
+
+ `newtype` and `data` on the other hand, create genuinely new types. `newtype` is basically just an efficient version of `data` that you can use in special circumstances. `newtype` must always take one type argument and have one value constructor. For example:
newtype PersonalData a = PD a
You could also say:
- data PersonalData a = PD a
+ data PersonalData2 a = PD2 a
- And `data` also allows multiple type arguments, and multiple variants and value constructors.
+ And `data` also allows multiple type arguments, and multiple variants and value constructors. <!-- Subtle difference: whereas `PersonalData a` is isomorphic to `a`, `PersonalData2 a` has an additional value, namely `PD2 _|_`. In a strict language, this is an additional type an expression can have, but it would not be a value. -->
OCaml just uses the one keyword `type` for all of these purposes:
* When a type only has a single variant, as with PersonalData, Haskell programmers will often use the same name for both the type and the value constructor, like this:
- data PersonalData a = PersonalData a
+ data PersonalData3 a = PersonalData3 a
The interpreter can always tell from the context when you're using the type name and when you're using the value constructor.
For more details, see:
- * [Haskell Wikibook on do-notation](http://en.wikibooks.org/wiki/Haskell/do_Notation)
+ * [Haskell wikibook on do-notation](http://en.wikibooks.org/wiki/Haskell/do_Notation)
* [Do-notation considered harmful](http://www.haskell.org/haskellwiki/Do_notation_considered_harmful)
* If you like the Haskell do-notation, there's [a library](http://www.cas.mcmaster.ca/~carette/pa_monad/) you can compile and install to let you use something similar in OCaml.