[Haskell-cafe] Why is this strict in its arguments?
pirelo at googlemail.com
Wed Dec 5 04:01:01 EST 2007
Hasn't Ryan raised an interesting point, though?
Bottom is used to denote non-termination and run-time errors. Are they
the same thing? To me, they're not. A non-terminating program has
different behaviour from a failing program.
When it comes to strictness, the concept is defined in a particular
semantic context, typically an applicative structure:
[[ f x ]] = App [[f]] [[x]]
Function f is strict if App [[f]] _|_ = _|_
Yet, that definition is pinned down in a semantics where what _|_
models is clearly defined.
I don't see why one could not provide a more detailed semantics where
certain kinds of run-time errors are distinguished from bottom.
Actually, this already happens. Type systems are there to capture many
program properties statically. Some properties that can't be captured
statically are captured dynamically: the compiler introduces run-time
tests. Checking for non-termination is undecidable, but putting
run-time checks for certain errors is not.
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