?

[Christopher Morgan]

Jay,

What are the definitions of strong and safe in the context of type systems? What is important to know about them?  

I can't parse my notes on the subject and i feel like your definition is more concise than the one given in the book.

Thanks,

Christopher

[Jay McCarthy]

Strong has no meaning.

Safe means that it will not actually perform erroneous operations. Erroneous means violating abstractions such as that numbers, booleans, and strings are distinct. C is unsafe because you can add numbers to strings. Java is not because you can't. Even JavaScript is not, because although it allows "100" + 1, it gives that a meaning that it is faithful to.

Jay

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Jay McCarthy <j...@cs.byu.edu>
Assistant Professor / Brigham Young University
http://faculty.cs.byu.edu/~jay

"The glory of God is Intelligence" - D&C 93

[Christopher Morgan]

Thanks! 

Instead of strong i meant to ask about sound, sorry. Sound?

~Chris

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[Jay McCarthy]

Sound means the static type system accurately predicts the dynamic behavior of the system. If the type system says an expression is of type Bool, then it really will return a Bool, modulo running forever or throwing "acceptable" errors, such as Div by 0.

[Christopher Morgan]

Thanks! I appreciate it.

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