March 2014 update

Task/Mutual-recursion/Ada/mutual-recursion-2.ada

@@ -0,0 +1,20 @@
+with Ada.Text_Io; use Ada.Text_Io;
+procedure Mutual_Recursion is
+   function M(N: Natural) return Natural;
+   function F(N: Natural) return Natural;
+
+   function M(N: Natural) return Natural is
+       (if N = 0 then 0 else N – F(M(N–1)));
+
+   function F(N: Natural) return Natural is
+       (if N =0 then 1 else N – M(F(N–1)));
+begin
+   for I in 0..19 loop
+      Put_Line(Integer'Image(F(I)));
+   end loop;
+   New_Line;
+   for I in 0..19 loop
+      Put_Line(Integer'Image(M(I)));
+   end loop;
+
+end Mutual_recursion;

Task/Mutual-recursion/D/mutual-recursion.d

@@ -1,14 +1,14 @@
 import std.stdio, std.algorithm, std.range;
 
-/*auto*/ int male(in int n) pure nothrow {
-    return n ? (n - female(male(n - 1))) : 0;
+int male(in int n) pure nothrow {
+    return n ? n - male(n - 1).female : 0;
 }
 
-/*auto*/ int female(in int n) pure nothrow {
-    return n ? (n - male(female(n - 1))) : 1;
+int female(in int n) pure nothrow {
+    return n ? n - female(n - 1).male : 1;
 }
 
 void main() {
-    iota(20).map!female().writeln();
-    iota(20).map!male().writeln();
+    20.iota.map!female.writeln;
+    20.iota.map!male.writeln;
 }

Task/Mutual-recursion/Objective-C/mutual-recursion.m

@@ -1,6 +1,6 @@
-#import <objc/Object.h>
+#import <Foundation/Foundation.h>
 
-@interface Hofstadter : Object
+@interface Hofstadter : NSObject
 + (int)M: (int)n;
 + (int)F: (int)n;
 @end

Task/Mutual-recursion/Perl/mutual-recursion.pl

@@ -1,13 +1,7 @@
-use strict;
-use warnings;
+sub F { my $n = shift; $n ? $n - M(F($n-1)) : 1 }
+sub M { my $n = shift; $n ? $n - F(M($n-1)) : 0 }
 
-# For mutually recursive functions,
-# predeclaring is probably a good idea.
-sub M; sub F;
-
-sub F { my $n = shift; $n ? $n - M F $n-1 : 1 }
-sub M { my $n = shift; $n ? $n - F M $n-1 : 0 }
-
-for my $f (\&F, \&M) {
-    print join(' ', map $f->($_), 0 .. 19), "\n";
+# Usage:
+foreach my $sequence (\&F, \&M) {
+    print join(' ', map $sequence->($_), 0 .. 19), "\n";
 }

Task/Mutual-recursion/Rust/mutual-recursion.rust

@@ -0,0 +1,25 @@
+fn f(n: int) -> int {
+    match n {
+        0 => 1,
+        _ => n - m(f(n - 1))
+    }
+}
+
+fn m(n: int) -> int {
+    match n {
+        0 => 0,
+        _ => n - f(m(n - 1))
+    }
+}
+
+fn main() {
+    for i in range(0, 20).map(f) {
+        print!("{} ", i);
+    }
+    println!("")
+
+    for i in range(0, 20).map(m) {
+        print!("{} ", i);
+    }
+    println!("")
+}

Task/Mutual-recursion/TXR/mutual-recursion.txr

@@ -1,37 +1,13 @@
-@(define f (n out))
-@  (local n1 fn1 mfn1)
-@  (cases)
-@    (bind n "0")
-@    (bind out "1")
-@  (or)
-@    (next `!echo $(( @n - 1 ))`)
-@    n1
-@    (f n1 fn1)
-@    (m fn1 mfn1)
-@    (next `!echo $(( @n - @mfn1 ))`)
-@    out
-@  (end)
-@(end)
-@(define m (n out))
-@  (local n1 mn1 fmn1)
-@  (cases)
-@    (bind n "0")
-@    (bind out "0")
-@  (or)
-@    (next `!echo $(( @n - 1 ))`)
-@    n1
-@    (m n1 mn1)
-@    (f mn1 fmn1)
-@    (next `!echo $(( @n - @fmn1 ))`)
-@    out
-@  (end)
-@(end)
-@(next `!seq 0 15`)
-@(collect :vars ())
-@  n
-@  (f n fn)
-@  (m n mn)
-@  (output)
-f(@n) = @fn; m(@n) = @mn
-@  (end)
-@(end)
+@(do
+   (defun f (n)
+     (if (>= 0 n)
+       1
+       (- n (m (f (- n 1))))))
+
+   (defun m (n)
+     (if (>= 0 n)
+       0
+       (- n (f (m (- n 1))))))
+
+   (each ((n (range 0 15)))
+     (format t "f(~s) = ~s; m(~s) = ~s\n" n (f n) n (m n))))