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Write a perfectly legal code in a decent language of your choice whose compiling will either crash the compiler or send it into an infinite loop (infinite compile time).


  • Use a standard language that is used in real world.
  • Use a standard, well-developed compiler (no answers like "I wrote my C compiler that crashes on everything").
  • The code must be legal in the language (so most likely you'll have to exploit a compiler or a language bug).
  • Give your compiler version and options used so that others can replicate it.
  • Explain why the compiler crashed, if possible.

Have fun :)

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Could you elaborate on what you mean by "crash"? –  GigaWatt Sep 6 '12 at 19:45
@GigaWatt I mean that the compiler stops in an uninteded way. Neither by successfully compiling the input nor by issuing an error message. It has to really crash, like segfault, eating up all the memory, throwing an unchecked exception etc. –  Petr Pudlák Sep 6 '12 at 19:50
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9 Answers

up vote 8 down vote accepted

I'm pretty sure it's been fixed now, but it used to be that you could crash the Java compiler (or, crash Eclipse) by writing

class Foo {
  static double d = 2.2250738585072012e-308;


Actually, according to that page, the compiler will just hang, not crash. Still, I thought that was pretty fun.

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My favorite solution for GHC:

data Bad a = C (Bad a -> a)

xx :: Bad a -> a
xx (x@(C x')) = x' x

omega :: a
omega = xx (C xx)

main = omega

For GHC 6.12.1 both ghci Bad.hs and ghc Bad.hs loop infinitely. GHC 7.4.1 loops infinitely when ghc -O2 Bad.hs is executed.

Explanation: omega is defined using an infinite recursion (the only way it can inhabit any type). Compiler's inliner sees xx as a simple, non-recursive function, so it tries to inline it in the definition of omega. It results in (\x@(C x') -> x' x) (C xx). Seeing a pattern match on a constructor the compiler tries to reduce it, getting xx (C xx) again and loops. The trick is that xx is actually recursive, but the recursion is hidden within the data type.

Note: While writing the puzzle, I forgot I left GHC running in the infinite loop. It took all my memory, crashed Firefox and I barely managed to kill it without hard reset.

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+1 just for the trouble you went through for the answer :P –  UnkwnTech Sep 6 '12 at 21:13
@UnkwnTech :-) Actually I discovered this by an accident when trying to implement recursion using a recursive data type only. –  Petr Pudlák Sep 6 '12 at 21:17
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how about if you can crash the IDE by typing in code?

in any Microsoft Office application, try this:

ALT+F11 to get to the VBA window, then try the following code

sub foo()
dim v(1 to 3, 1 to 3)
redim preserve v(,1 to 5)

and behold:

Excel Death

You can simply type redim preserve v(,1 to 5) into the immediate window, and it will crash after you press ENTER !

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nice, but more like "crash your favourite interpreter" –  mbx Sep 7 '12 at 20:16
Could I get a quick rundown on why this works? –  GigaWatt Jan 7 '13 at 16:23
@GigaWatt, it's discussed in a little more depth here, but it appears that the IDE cannot cope with errors (unexpected symbol , and expected ,) –  Sean Cheshire Jan 7 '13 at 20:28
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This is easy in any dependently-typed language. Type-checking general dependent types is undecidable since it may require arbitrarily complex computations (Turing-complete). You can simply encode in a dependent type a too-large value. Then the type-checker will use all available memory and crash. For instance, in Coq, ReyCharles gives the example of Compute 70000., which causes the type-checker to construct a giant Peano numeral and crash.

In more common languages that support some sort of macro expansion or metaprogramming, you can do something similar. For example, you can use all available memory in C:

#include <stdio.h>
#define a printf("%s", "Hello, world!\n");
#define b a a a a a a a a a a a a a a a a
#define c b b b b b b b b b b b b b b b b
#define d c c c c c c c c c c c c c c c c
#define e d d d d d d d d d d d d d d d d
#define f e e e e e e e e e e e e e e e e
// ...
#define z y y y y y y y y y y y y y y y y
int main() { z }

The D programming language allows compile-time function execution. This can be used to compute something at compile time that is too large to fit in memory. Something similar can be achieved using C++ template metaprogramming.

In XML (not a compiled programming language, but an XML processor is analogous to a compiler), expanding entities can make the processor run out of memory:

<?xml version="1.0"?>
<!DOCTYPE lolz [
 <!ENTITY lol "lol">
 <!ENTITY lol1 "&lol;&lol;&lol;&lol;&lol;&lol;&lol;&lol;&lol;&lol;">
 <!ENTITY lol2 "&lol1;&lol1;&lol1;&lol1;&lol1;&lol1;&lol1;&lol1;&lol1;&lol1;">
 <!ENTITY lol3 "&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;&lol2;">

This is called the billion laughs attack.

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+1 for the "billion laughs attack" - what a name –  Bojangles Apr 21 '13 at 6:57
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Perl (15)

BEGIN{1while 1}

This creates an infinite loop at compile time:

A BEGIN code block is executed as soon as possible, that is, the moment it is completely defined, even before the rest of the containing file (or string) is parsed.

(from perlmod)

And that's why Perl isn't able to complete parsing the code. This doesn't terminate:

$ perl -MO=Deparse -e 'BEGIN{1while 1}'
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This segfaults the J interpreter (at least on Linux):


It tries to read from memory address 2. Interestingly, if you try it with 0 or 1, you get domain error.

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TeX is a macro-expansion language. Here we define the expansion of the macro \x to be \x again, and then we add afterwards an invocation of \x. TeX gets stuck endlessly replacing \x with \x.

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Common Lisp

Macros make it easy:

(defmacro loop-forever ()
  (loop for x from 0 collecting x))

(defun compile-me ()

Compiling compile-me calls loop-forever, which exhausts heap memory during its expansion and crashes the compiler. If you just want to make the compiler hang indefinitely, then this definition of loop-forever will do it:

(defmacro loop-forever ()

This should work using any CL implementation, unless yours is extremely clever and can detect simple infinite loops, but I seriously doubt any do this. Full protection against this is impossible, of course.

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Smalltalk (Squeak dialect, version 4.x)

Very easy, just evaluate this, or accept a method with this literal


It will try to evaluate the power of 10 in Large Integer arithmetic, just for correctly rounding inf Tsss ;)

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