On 12/4/2019 11:03 AM, Dominik Pantůček wrote
looking at vector-length[1] documentation, it returns (exact-nonnegative-integer?). However, as far as I can tell, it returns (fixnum?). Also for subsequent contracts in the vector's documentation all indices are assumed to be (exact-nonnegative-integer?) but usually it is impossible on given platform to use anything larger than (fixnum?) in reality
You are correct that (exact-nonnegative-integer?) doesn't limit values to fixnum range, but the point of using it is more to exclude negative values than to allow super large positive ones.
This question - or something substantially similar - has come up before. Your question is about contracts - which can be used from plain Racket - but it is noteworthy that typed/Racket provides types for positive, negative, nonpositive, and nonnegative fixnums - but there are no built-in tests for any of these, so a suitable contract or type declaration has to be synthesized using multiple tests.
For example on 64bit platforms the (fixnum?) could store numbers from (- (expt 2 62)) to (sub1 (expt 2 62)). Vector slots cannot be smaller than 64bits (machine-dependent pointers) which means 8 bytes = 3 bits of address. Given 64bit (VERY theoretical) size of the address space, this leaves the possibility of storing a single vector with (expt 2 61) elements into the memory. If I did not overlook anything, the contracts could be safely changed to (fixnum?).
It would be more correct to use (and/c fixnum? (or/c zero? positive?)) to explicitly limit the value.
And yes, I found this issue while cleaning up my futures-sort[2] package discussed a few months ago here. If I assume (exact-nonnegative-integer?), I need to manually check for (fixnum?). Even though it - given the information above - does not really make much sense. Should I open a PR?
I don't remember how the previous discussions went. I'm not sure anything ever really was resolved.
Cheers, Dominik [1] https://docs.racket-lang.org/reference/vectors.html#(def._((quote._~23~25kernel)._vector-length)) [2] https://docs.racket-lang.org/futures-sort/index.html
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