[OT] What should be in a programming language?

[Jason House]

I've been thinking lately about what my ideal programming language would look like and what I might write if I tried to create one. Below is a short list of big things I'd do. What do you think of my ideas? What would you do?

I'd look to D and Scala for inspiration, but want to allow better reasoning about code.

I'd use D's transitive const and use transitive pure instead of transitive immutable.

Functions can't effect glabal variables unless marked as such. I'll have to learn what a monad is so that some side effects can be hidden? 

By default, a function can not keep its variables past function scope. If a parameter or local variable is to remain for longer it must be marked as such in its type.

Similarly, all function arguments will default to (transitive) const. Any mutable arguments must be marked as such. I'm unsure if ref arguments should come in a final and non-final form. One nice side effect of this is that value types vs. reference types don't require special consideration.  

I'd probably do away with out arguments in favor of return tuples.

All types are not nullable by default. T and T? seem reasonable enough. I'd probably twist that a bit and use a beefed up variable declaration similar to scala. "pure? x: T = ..." would be a nullable immutable variable of type T.

Compile time capabilities would exceed D's. I'm thinking of a simple marker to make anything compile time (i.e. #). #if would be like static if. #pure would be a manifest constant. An array with some compile time values would be easy [foo(7), #bar(8)]. This also means #switch and #foreach would exist (among other things). Generics with compile time arguments become templates.

I would have a type type, usable for both compile time and run time reflection.

I've probably forgotten a number of basic things, but that should be enough for now.