Am 19.10.2011 20:23, schrieb Andrew Pennebaker: > Practical uses for referencable anonymous functions:
For such applications one uses procedure variables in pascal. > > (map f collection) > > This is the prototypical way to run a function over each element in a > collection, returning the results. > > Example: > > (map (lambda (x) (+ x 1)) '(1 2 3)) > > -> (2 3 4) > > (sort compare collection) > > When dealing with complex data types, the user may want to implement a > custom compare function. > > (sort (lambda (x y) (- y:employee-id x:employeeid)) (list emp1 emp2 emp3)) > > -> (emp3 emp1 emp2) > > (zip f collection1 collection2) > > Similar to map, zip runs a 2-input function over the elements of the > collections, returning the results. > > (zip (lamba (x y) (+ x y)) '(1 2 3) '(4 5 6)) > > -> (5 7 9) > > At first glance, each of these examples may seem pointless. Can't we > implement the same behavior without referencing anonymous functions? > Yes, we can, but only for a specific function. If you want your database > library to allow users to customize sorting, you'll need referencable > anonymous functions. I still don't see why this cannot be done by procedure variables: one can easily pass a procedure reference to a compare function to any sort library call. The example is far from explaining why it is needed to be able to return a reference to an anonymous method to the outside of the enclosing function. _______________________________________________ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
