[Haskell-cafe] Re: Would someone explain this code to me?
> > What I don't understand is his use of the "T" constructor, both at > > > > insertSet x s = T B a y b > > Here it creates a new RedBlackSet > > > and in the where statement: > > > > T _ a y b = ins s > > Here it's a pattern match. So if ins s returns (T x a' y' > b'), then a = a'; y = y'; b = b' are used in the expresion > covered by the where clause. If you're wondering how the compiler tells the difference, have a look at section 2.4 of the Haskell 98 Report (Identifiers and Operators). Roughly, an identifier beginning with a lowercase letter or underscore must be a variable identifier, while an identifier beginning with an uppercase letter must be a constructor identifier. In other words, the second example above cannot be the definition of a function called "T", because "T" cannot be the name of a function. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Would someone explain this code to me?
On 06 Dec 2006 19:33:51 +, Jón Fairbairn <[EMAIL PROTECTED]> wrote: > and in the where statement: > > T _ a y b = ins s Here it's a pattern match. So if ins s returns (T x a' y' b'), then a = a'; y = y'; b = b' are used in the expresion covered by the where clause. Great, thanks for clearing that up. Sometimes Haskell is a bit too concise! Justin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Would someone explain this code to me?
"Justin Bailey" <[EMAIL PROTECTED]> writes: > I'm reading Chris Okasaki's "Purely Functional Data Structures", and some > of his Haskell is confusing me. He defines the type Color and RedBlackSet > as: > > data Color = R | B > data RedBlackSet a = E | T Color (RedBlackSet a) a (RedBlackSet a) > > and then later he defines a function insertSet: > > insertSet x s = T B a y b > where ins E = T R E x E > ... > T _ a y b = ins s > > What I don't understand is his use of the "T" constructor, both at > > insertSet x s = T B a y b Here it creates a new RedBlackSet > and in the where statement: > > T _ a y b = ins s Here it's a pattern match. So if ins s returns (T x a' y' b'), then a = a'; y = y'; b = b' are used in the expresion covered by the where clause. -- Jón Fairbairn [EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
