[Haskell-cafe] Avoiding "Non-exhaustive patterns in function f"

[peterv]

Haskell is known for its very strong static type checking, which eliminates
a lot of runtime errors.

 

But the following simple program crashes at runtime:

 

data D = A | B

f A = True

main = print (f B)

 

I understand this has nothing to do with type checking, but why can't the
compiler give a warning about this? Or is this by design or because it is
impossible to check with more complex recursive data types?

 

Thanks,

Peter

 

 

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