Shooting your self in the foot
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The following list was proposed by members of Haskell-Cafe.
The original thread can be found here.
How to Shoot Your Self in the Foot With Haskell: Putting the unsafe in unsafePerformIO!
- You shoot the gun, but the bullet gets trapped in the IO monad.
- Couldn't match expected type 'Deer' against inferred type 'Foot'.
- While compiling your program the compiler produces a type error long enough to overflow a kernel buffer, overwrite the trigger control register and shoot you in the foot.
- After trying to decipher the type errors from the compiler, your head explodes.
- After you've finally found a way to circumvent the type system and shoot yourself in the foot, Oleg appears out of nothing and shoots you in the foot for coming up with it before him.
- You shoot the gun but nothing happens (Haskell is pure, after all).
- Your foot is fine, until you try to walk on it, at which point it becomes mangled.
- You have a shootFoot function which you've proven correct. QuickCheck validates it for arbitrary you-like values. It will be evaluated only when you end up at the hospital. You hope this doesn't come to pass, as it actually returns a bullet-ridden copy of yourself and you don't want to be garbage-collected.
foreign import ccall "shootparts.h shootfoot" shoot_foot :: Gun -> Programmer -> IO ()
shootSelfInFoot = unsafePerformIO . shoot . foot $ self -- Shoot self in foot 0 or more times depending on evaluation order
- No instance for (Target Foot)
arising from use of `shoot' at SelfInflictedInjury.hs:1:0
Possible fix: add an instance declaration for (Target Foot)
In the expression: shoot foot
- You go to shoot yourself in the foot but the bullet is in the ST monad and the gun is in the IO monad, so you can't.
- You ask Haskell to shoot you in the foot but by the rules of lazy evaluation you don't need the result yet so it doesn't happen.
- You decide to shoot yourself in the foot but get distracted devising a ballistics algebra and wondering if you can do the calculations in the type system.
- You want to shoot yourself in the foot but realize there is no Gun datatype so use Arrows instead.
- You shoot in the direction of your foot, but since you are inside the STM monad you can just retry until you figure out what to do.
- You shoot yourself in the foot, but you are perfectly fine as long you just don't evaluate the foot.
- You shoot yourself in the foot, but nothing happens unless you start walking.
- Don't forget about memory consumption! If you don't look, the bullet causes heap overflow. If you look, the bullet causes stack overflow.
- You *appear* to have deliberately shot yourself in the foot, and yet your program actually runs perfectly OK due to lazy evaluation. (So long as you remember to not look at your foot...)
- You aim the gun at your foot, pull the trigger and remove the clip. When you look at your undamaged foot, the hammer clicks on an empty barrel.