TypeCheck.jl

I didn't claim it was. That's one of the tradeoffs you make in exchange for a simpler, more forgiving programming model (and the ability to do serious work in a REPL or notebook). However, given that Julia programs can be mostly type inferred before execution, it is possible to check for this kind of error before running a program. There have been some projects to do exactly that [1] [2], and I suspect that once Julia reaches 1.0, we'll focus more effort on static analysis tools. The point is that you don't need a static language to get many of the benefits of types, you just need your language that allows you to express type-based properties. One of the way to do that is to have a set of formal rules for deriving the type of every expression in a program, but that's not actually necessary. [1] https://github.com/astrieanna/TypeCheck.jl [

It is unmaintained now, but you might want to have a look at [1], which builds on the type inference system to add some static checks. I believe there may also be some related work in [2]. > Then again, maybe nobody else has these issues and I'm just bad at deducing when AbstractVector can't be used. Nope, not just you. This is definitely an issue. [1] https://github.com/astrieanna/TypeCheck.jl [2] https://github.com/tonyhffong/Lint.jl

For some of the stuff about types and optimisation in particular, you should check out Julia's type system [0]. First-class types, avoiding inheritance, optional type restrictions, and (albeit early) support for static checking [1], it's all there. It'd be worth taking a look at things like its macros as well – I actually think Julia hits on a lot of the points in this post really well, though of course no language is perfect. [0] http://docs.julialang.org/en/latest/manual/types/ [1] https://github.com/astrieanna/TypeCheck.jl Minor nitpick: > Tut, tut. That should really be a set! It’s much faster, O(1). Structures like sets have a lower complexity but higher constants (i.e. the overhead of hashing the value etc). When you have a small number of values, a straight linear search over an array will often be faster (which is why it's useful