Javascript

Perl

% perl -le 'print 0**0'
1

複素数にしても駄目。

#!/usr/bin/env perl -l
use strict;
use Math::Complex;
my $z0 = cplx(0,0);
print "$z0 ** $z0 == ", $z0**$z0;

%perl cpow.pl
0 ** 0 == 1

Ruby

% ruby -e 'p 0**0'
1

#!/usr/bin/env ruby
include Math
require 'complex'
z0 = Complex(0,0);
p z0**z0
puts z0**z0

% ruby cpow.rb
Complex(1, 0)
1+0i

Python

% python -c 'print 0**0'
1

C

厳密にはlibm。C++は省略。

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
int main(int argc, char **argv){ 
    double x = argc > 1 ? atof(argv[1]) : 0.0;
    double y = argc > 2 ? atof(argv[2]) : 0.0;
    return printf("pow(%f, %f) == %f\n",x, y, pow(x,y)); 
}

% gcc -Wall -W -lm -o pow pow.c
% ./pow 
pow(0.000000, 0.000000) == 1.000000

scheme

実装はgauche

% gosh
gosh> (expt 0 0)
1

Haskell

% ghci
   ___         ___ _
  / _ \ /\  /\/ __(_)
 / /_\// /_/ / /  | |      GHC Interactive, version 6.6, for Haskell 98.
/ /_\\/ __  / /___| |      http://www.haskell.org/ghc/
\____/\/ /_/\____/|_|      Type :? for help.

Loading package base ... linking ... done.
Prelude> 0^0
1
Prelude> 0**0
1.0

bc

% bc
bc 1.06
Copyright 1991-1994, 1997, 1998, 2000 Free Software Foundation, Inc.
This is free software with ABSOLUTELY NO WARRANTY.
For details type `warranty'. 
0^0
1

こうなってくると、累乗をサポートしていてかつ0**0!=1な言語が存在しないかとても気になる。もちろんそういうクラスやプロトタイプで実装するのはたいていの言語では簡単にできるのではあるのだけど。

Dan the Nullingual Powered by Null

追記:

例えば C99 (ISO/IEC 9899;1999) の math.h に含まれる pow 関数は，底と指数の両方に 0 が与えられた場合，ドメインエラーを返すと定義されている [C99] 。

これ、「ドメインエラーを返す場合もある」ですね。原文は以下のとおり。

The pow functions compute x raised to the powery. A domain error occurs if x is finite and negative and y is finite and not an integer value. A range error may occur. A domain error may occur if x is zero and y is zero. A domain error or range error may occur if x is zero andyis less than zero.

で、GCCではこんな感じです。

     pow(x, +-0) returns 1 for any x, even a NaN.

     The function pow(x, 0) returns x**0 = 1 for all x including x = 0, infin-
     ity, and NaN .  Previous implementations of pow may have defined x**0 to
     be undefined in some or all of these cases.  Here are reasons for return-
     ing x**0 = 1 always:

     1.      Any program that already tests whether x is zero (or infinite or
             NaN) before computing x**0 cannot care whether 0**0 = 1 or not.
             Any program that depends upon 0**0 to be invalid is dubious any-
             way since that expression's meaning and, if invalid, its conse-
             quences vary from one computer system to another.

     2.      Some Algebra texts (e.g. Sigler's) define x**0 = 1 for all x,
             including x = 0.  This is compatible with the convention that
             accepts a[0] as the value of polynomial

                   p(x) = a[0]*x**0 + a[1]*x**1 + a[2]*x**2 +...+ a[n]*x**n

             at x = 0 rather than reject a[0]*0**0 as invalid.

     3.      Analysts will accept 0**0 = 1 despite that x**y can approach any-
             thing or nothing as x and y approach 0 independently.  The reason
             for setting 0**0 = 1 anyway is this:

                   If x(z) and y(z) are any functions analytic (expandable in
                   power series) in z around z = 0, and if there x(0) = y(0) =
                   0, then x(z)**y(z) -> 1 as z -> 0.

     4.      If 0**0 = 1, then infinity**0 = 1/0**0 = 1 too; and then NaN**0 =
             1 too because x**0 = 1 for all finite and infinite x, i.e., inde-
             pendently of x.