Time for an 2014 update…

Task/Y-combinator/D/y-combinator.d

@@ -1,31 +1,25 @@
 import std.stdio, std.traits, std.algorithm, std.range;
 
-auto Y(F)(F f) {
-  alias D = void delegate();
-  alias Ret = ReturnType!(ParameterTypeTuple!F);
-  alias Args = ParameterTypeTuple!(ParameterTypeTuple!F);
-
-  return ((Ret delegate(Args) delegate(D) x) =>
-    x(cast(D)x))(
-      (D y) =>
-        f((Args args) =>
-          (cast(Ret delegate(Args))(cast(D delegate(D))y)(y))(args)
-        )
-    );
+auto Y(S, T...)(S delegate(T) delegate(S delegate(T)) f) {
+    static struct F {
+        S delegate(T) delegate(F) f;
+        alias f this;
+    }
+    return (x => x(x))(F(x => f((T v) => x(x)(v))));
 }
 
-void main() { // Demo code --------------------
-  auto factorial = Y((int delegate(int) self) =>
-    (int n) => 0 == n ? 1 : n * self(n - 1)
-  );
+void main() { // Demo code:
+    auto factorial = Y((int delegate(int) self) =>
+        (int n) => 0 == n ? 1 : n * self(n - 1)
+    );
 
-  auto ackermann = Y((ulong delegate(ulong, ulong) self) =>
-    (ulong m, ulong n) {
-      if (m == 0) return n + 1;
-      if (n == 0) return self(m - 1, 1);
-      return self(m - 1, self(m, n - 1));
+    auto ackermann = Y((ulong delegate(ulong, ulong) self) =>
+        (ulong m, ulong n) {
+            if (m == 0) return n + 1;
+            if (n == 0) return self(m - 1, 1);
+            return self(m - 1, self(m, n - 1));
     });
 
-  writeln("factorial: ", 10.iota.map!factorial);
-  writeln("ackermann(3, 5): ", ackermann(3, 5));
+    writeln("factorial: ", 10.iota.map!factorial);
+    writeln("ackermann(3, 5): ", ackermann(3, 5));
 }

Task/Y-combinator/Deja-Vu/y-combinator.djv

@@ -23,5 +23,5 @@ labda f:
 			1
 set :fib Y
 
-. fac 6
-. fib 6
+!. fac 6
+!. fib 6

Task/Y-combinator/Ruby/y-combinator-1.rb

@@ -1,14 +1,11 @@
-irb(main):001:0> Y = lambda do |f|
-irb(main):002:1*   lambda {|g| g[g]}[lambda do |g|
-irb(main):003:3*                       f[lambda {|*args| g[g][*args]}]
-irb(main):004:3>                     end]
-irb(main):005:1> end
-=> #<Proc:0x00000204f5e6e0@(irb):1 (lambda)>
-irb(main):006:0> Fac = lambda{|f| lambda{|n| n < 2 ? 1 : n * f[n-1]}}
-=> #<Proc:0x00000202a88aa0@(irb):6 (lambda)>
-irb(main):007:0> Array.new(10) {|i| Y[Fac][i]}
-=> [1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880]
-irb(main):008:0> Fib = lambda{|f| lambda{|n| n < 2 ? n : f[n-1] + f[n-2]}}
-=> #<Proc:0x00000201a968b8@(irb):8 (lambda)>
-irb(main):009:0> Array.new(10) {|i| Y[Fib][i]}
-=> [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
+y = lambda do |f|
+  lambda {|g| g[g]}[lambda do |g|
+      f[lambda {|*args| g[g][*args]}]
+    end]
+end
+
+fac = lambda{|f| lambda{|n| n < 2 ? 1 : n * f[n-1]}}
+p Array.new(10) {|i| y[fac][i]}   #=> [1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880]
+
+fib = lambda{|f| lambda{|n| n < 2 ? n : f[n-1] + f[n-2]}}
+p Array.new(10) {|i| y[fib][i]}   #=> [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]

Task/Y-combinator/Ruby/y-combinator-2.rb

@@ -4,10 +4,10 @@ def y(&f)
   end.tap {|g| break g[g]}
 end
 
-Fac = y {|&f| lambda {|n| n < 2 ? 1 : n * f[n - 1]}}
-Fib = y {|&f| lambda {|n| n < 2 ? n : f[n - 1] + f[n - 2]}}
+fac = y {|&f| lambda {|n| n < 2 ? 1 : n * f[n - 1]}}
+fib = y {|&f| lambda {|n| n < 2 ? n : f[n - 1] + f[n - 2]}}
 
-p Array.new(10) {|i| Fac[i]}
+p Array.new(10) {|i| fac[i]}
 # => [1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880]
-p Array.new(10) {|i| Fib[i]}
+p Array.new(10) {|i| fib[i]}
 # => [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]