April Fools Jokes [closed]

Question

Figure out how to mess up another programmer's project by making a subtle, hard to find (but "harmless") "bug". (Double quotes FTW!)

Try to keep them short; shorter ~= subtle.

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For example:

#define true false

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Don't actually destroy the code directly. For example, from this:

for(size_t i = 0; i < 10; ++i)

To:

for(size_t *i = new size_t; ++i; delete i)

Or even:

for(size_t i = 0; i <= 10; ++i)

Is not OK. If a language actually allows you to change < to <= without changing that code "directly", then it's alright. (You know what I mean. Deleting all the code is just

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Voting

Up vote the most original/creative/subtle solutions.

On Mother's Day (May 8, 2011), the most up voted answer will be chosen as the winner.

Answer 1

#define if(x) if(random(100) > 0 && (x))

Answer 2

Haskell

module UnsafePrelude where

import Prelude hiding ((.), (+), (-), sum, map, foldl)
import qualified Prelude as P

import Unsafe.Coerce

-- disallow (f . g . h)
infix 9 .
(.) = (P..)

-- Make arithmetic a bit more exciting.
-- These actually work correctly for trivial Int and Integer cases,
-- at least in GHC 6.12.1 on x86.
(+), (-) :: (Num a) => a -> a -> a
(+) = unsafeCoerce ((P.+) :: Float -> Float -> Float)
(-) = unsafeCoerce ((P.-) :: Float -> Float -> Float)

sum :: (Num a, Num b) => [a] -> b
sum = unsafeCoerce (P.sum :: [Float] -> Float)

-- Make map a little less type-safe.
map :: (a -> b) -> [c] -> [b]
map   = unsafeCoerce P.map

-- Make foldl associate the wrong way, but still have the same type.
foldl :: (a -> b -> a) -> a -> [b] -> a
foldl f = foldr (flip f)

Answer 3

GolfScript

1: 

Note there is a space after the colon. This assigns the value 1 to the space character. All further code that uses the space for readability will find unexpected extra ones on its stack!

Alternatively,

0:1

assigns the value 0 to the character 1.

Answer 4

Ruby

class Fixnum
    alias add +
    def + (n)
        add n.add 1
    end
end

And now, like in 1984...

(33):0>  2 + 2 == 5
>>> true
(36):0>