Jim Pryor scripsit: > Lists are *a* basic functional programming structure.
Yes, of course. What I meant was, "As between lists and pairs, it is lists that are the fundamental data structure." As you say, pairs are just a special case of tuples which happen to be used to implement lists in Lisp/Scheme. > Conceptually, a list is type-homogeneous, I don't agree here: see below. > If you map some function that accepts either ints or bools as arguments > over your list, then the list can be regarded as homogeneously having > a union type, int-or-bool. In statically-typed functional languages, > you'd have to express that explicitly, by boxing the elements inside > an Either-type. That's the fundamental difference between mainstream FPLs and something like Typed Racket: an "Either string integer" type is not a supertype of "string" or "integer", whereas the Typed Racket equivalent "(U string integer)" is. So there is no need to unbox in Typed Racket: once you know what type you have using the STRING? or INTEGER? predicates, you can just use the ordinary operations on strings or integers as the case may be. Lisp/Scheme can, however, handle more complicated things that even Typed Racket can't (AFAIK) express, such as "an alternating list of symbols and arbitrary objects", also known as a property list. This is a special case of the truism that statically typed systems can and do reject programs (or make them impossible to express) that are entirely type-safe, because of the complexity of the types they use. -- First known example of political correctness: John Cowan After Nurhachi had united all the other http://www.ccil.org/~cowan Jurchen tribes under the leadership of the co...@ccil.org Manchus, his successor Abahai (1592-1643) issued an order that the name Jurchen should --S. Robert Ramsey, be banned, and from then on, they were all The Languages of China to be called Manchus. _______________________________________________ Chicken-users mailing list Chickenemail@example.com http://lists.nongnu.org/mailman/listinfo/chicken-users