src/test/run-pass/vec-matching-fold.rs

   1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11
  12 #![feature(advanced_slice_patterns)]
  13 #![feature(slice_patterns)]
  14
  15 use std::fmt::Debug;
  16
  17 fn foldl<T, U, F>(values: &[T],
  18                   initial: U,
  19                   mut function: F)
  20                   -> U where
  21     U: Clone+Debug, T:Debug,
  22     F: FnMut(U, &T) -> U,
  23 {    match values {
  24         &[ref head, ref tail..] =>
  25             foldl(tail, function(initial, head), function),
  26         &[] => {
  27             // FIXME: call guards
  28             let res = initial.clone(); res
  29         }
  30     }
  31 }
  32
  33 fn foldr<T, U, F>(values: &[T],
  34                   initial: U,
  35                   mut function: F)
  36                   -> U where
  37     U: Clone,
  38     F: FnMut(&T, U) -> U,
  39 {
  40     match values {
  41         &[ref head.., ref tail] =>
  42             foldr(head, function(tail, initial), function),
  43         &[] => {
  44             // FIXME: call guards
  45             let res = initial.clone(); res
  46         }
  47     }
  48 }
  49
  50 pub fn main() {
  51     let x = &[1, 2, 3, 4, 5];
  52
  53     let product = foldl(x, 1, |a, b| a * *b);
  54     assert_eq!(product, 120);
  55
  56     let sum = foldr(x, 0, |a, b| *a + b);
  57     assert_eq!(sum, 15);
  58 }