On Fri, Dec 29, 2006 at 02:06:32PM +0000, Paul Moore wrote:
Speaking as a relative newbie to Haskell, the thing that tripped me up was the fact that you can't have nested lists like the Lisp '(1 (2 (3 4) 5)) example in Haskell, because its type is not well-defined.
More precisely: You can't ununiformly nest standard [] lists. By ununiformly I mean: with leaves on different depths. You can do it with another list (or rather tree) implementation. You can nest [] lists uniformly, ie. [[1], [2,3,4]] is a nested list.
OTOH, it's not entirely clear to me if the issue would come up in "real" code.
It depends on what you mean by "issue". If syntactical overhead is an issue, then it comes up. For me it's a small issue, if at all.
Slinging about arbitrarily nested lists feels quite natural in Lisp, but isn't really idiomatic Haskell.
Nested lists are trees and using tree-like structures in Haskell is very idiomatic. Perhaps you would want some syntactic sugar for trees. If [] lists didn't have sugar in Haskell, they would be as "cumbersome" to use as trees. Best regards Tomasz