[Haskell-cafe] Datatypes - Haskell
Hello to everybody I am an new user of Haskel and generally in functional programming and I could say that I am very impressed from this Language. Though I can't understand the use of datatypes. Let's take a firly simple situtation e.g. data Pair a b = Pair a b i.e. an new type with name Pair parameterized over the types a,b with one Constructor named Paid which take two values of type a,b a more complex one would be data Either a b = Left a | Right b i.e a new type named Either parameterized over the types a, b and two Constructors 1. Left which take one value of type a and 2. Right which takes one value of type b I consider that the definitions above are well formulated. Nevertheless I can't understand them quite well. I have read that datatypes are used to define new structures. So, is there any corresponding example in C, sinch I am quite familiar with structures in it? I hope the word C here is allowed here :o) Thanks ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Datatypes - Haskell
On Feb 9, 2008, at 19:09 , Mattes Simeon wrote: e.g. data Pair a b = Pair a b struct Pair { a pair_a; b pair_b; }; data Either a b = Left a | Right b union Either { enum { Left, Right } _tag; a either_left; b either_right; }; (except that Haskell makes sure you use it properly, while C will let you access foo.either_right when foo._tag == Left). -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] [EMAIL PROTECTED] system administrator [openafs,heimdal,too many hats] [EMAIL PROTECTED] electrical and computer engineering, carnegie mellon universityKF8NH ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Datatypes - Haskell
On Feb 10, 2008 12:09 AM, Mattes Simeon <[EMAIL PROTECTED]> wrote: > Hello to everybody > > I am an new user of Haskel and generally in functional programming and I > could > say that I am very impressed from this Language. Though I can't understand > the > use of datatypes. > > Let's take a firly simple situtation > > e.g. data Pair a b = Pair a b > > i.e. an new type with name Pair parameterized over the types a,b with one > Constructor named Paid which take two values of type a,b > > a more complex one would be > data Either a b = Left a | Right b > > i.e a new type named Either parameterized over the types a, b and two > Constructors 1. Left which take one value of type a and 2. Right which > takes one > value of type b > > I consider that the definitions above are well formulated. Nevertheless I > can't > understand them quite well. > > I have read that datatypes are used to define new structures. So, is there > any > corresponding example in C, sinch I am quite familiar with structures in > it? I > hope the word C here is allowed here :o) > I guess C++ would be closer... template< class A, class B> struct Pair { A fst; B snd; } template< class A, class B> struct Either { enum {Left, Right} tag; union{ A left; B right; }; } In the second example the tag would be used to figure out which of the two alternatives the structure actually is. In Haskell you can just pattern match on the constructor. -- Sebastian Sylvan +44(0)7857-300802 UIN: 44640862 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe