[cap-talk] definition of the term "safe language"

[Matej Kosik]

Friends,

I was delighted to find a clear definition of the term
"safe language" in this book:
http://www.amazon.com/Types-Programming-Languages-Benjamin-Pierce/dp/0262162091/ref=sr_1_1?ie=UTF8&s=books&qid=1270548760&sr=8-1
According to Pierce:

"a safe language as one that protects its own abstractions.
Every high-level language provides abstraction of machine services.
Safety refers to the language's ability to guarantee the integrity
of these abstractions and of higher-level abstraction introduced
by the programmer using the definitional facilities of the language.
For example, a language may provide arrays, with access and update
operations, as an abstraction of the underlying memory.
A programmer using this language then expects that an array can be
changed only by using the update operation on it explicitly---and not,
for example, by writing past the end of some other data structure.
Similarly, one expects that lexically scoped variables can be accessed
only from within their scopes, that the call stack truly behaves like a
stack, etc.
In a safe language, such abstraction can be used abstractly;
in an unsafe language, they cannot: in order to completely understand
how a program may (mis)behave, it is necessary to keep in mind all sorts
of low-level details such as the layout of data structures in memory
and the order in which they will be allocated by the compiler.
In the limit, programs in unsafe languages may disrupt not only their
own data structures but even those of the run-time system;
the results in this case can be completely arbitrary."

I hope you like it as much as I did. :-)

The term "object-capability language" may then be a hyponym of the term
"safe language".