On 1/22/11 10:56 AM, Andre van Tonder wrote: > What I mean is that pattern matching often does not encourage good > abstraction. Which of the following is the better abstracted program > (independent of the underlying data type and independent of, for > example, adding new fields in data types )? > > (match data > ((record node l r) (traverse l) > (traverse r)) > ((leaf x) (display x)) > > or > > (cond ((node? data) (traverse (node-left data)) > (traverse (node-right data)) > ((leaf? data) (display (leaf-content data)) > > ML or Haskell programs are chock full of the former, which looks cool > exactly until they want to add an extra field to a data type and all of > a sudden realize that they have to change their whole program and all > programs that import the same types.
That doesn't *have* to be the case. Here's an example Racket program that uses pattern matching on a data type extended with an extra field: #lang racket (define-struct node (left right)) (define-struct (fancy node) (color)) (match (fancy 'l 'r 'c) [(node l r) (list l r)]) David _______________________________________________ r6rs-discuss mailing list r6rs-discuss@lists.r6rs.org http://lists.r6rs.org/cgi-bin/mailman/listinfo/r6rs-discuss
