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| use std::io; | |
| use std::util; | |
| enum List { | |
| Cons(uint,~List), | |
| Nil() | |
| } | |
| fn cons(x : uint, l : ~List) -> ~List{ | |
| return ~Cons(x,l); | |
| } | |
| fn printl(mut l : &~List) { | |
| io::print("("); | |
| loop { | |
| match l { | |
| &~Cons(x, ref next) => { | |
| l = next; | |
| io::print(fmt!("%u ",x)) | |
| } | |
| &~Nil() => break | |
| } | |
| } | |
| io::print(")"); | |
| } | |
| fn truncate<'r> (l: &'r mut ~List, N: uint) -> &'r mut ~List { | |
| if N == 0 { | |
| util::replace(l, ~Nil); | |
| } else { | |
| match **l { | |
| Cons(_, ref mut l) => { | |
| truncate(l, N - 1); | |
| } | |
| Nil => {} | |
| } | |
| } | |
| l | |
| } | |
| fn main() { | |
| let mut l = cons(1,cons(2,cons(3,~Nil))); | |
| printl(&l); | |
| io::print("\n"); | |
| printl(truncate(&mut l, 2)); | |
| io::print("\n"); | |
| } |
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