Walter put in a reasonable effort to sway me to his side of the fence last night. I'm still not entirely sold that implementation inside the language is necessary to achieve these details, but I don't have enough background into to argue, and I'm not the one that has to maintain the code :)

Here are some points we discussed... how do we do these (efficiently) in a library?

** Literal syntax.. and constant folding:

Constants and literals also need to be aligned. If we use array syntax to express literals, this will be a problem.

 int4 v = [ 1,2,3,4 ] + [ 5,6,7,8 ];

Any constant expressions need to be simplified at compile time: int4 vec = [ 6,8,10,12 ];

Perhaps this is possible with CTFE? Or will it be automatic if you express literals as if they were arrays?

** Expression interpretation/simplification:

 float4 v = -b + a;

Obviously, this should be simplified to 'a - b'.

 float4 v = a*b + c;

This should use a multiply-accumulate opcode on most architectures: FMADDPS v, a, b, c

** Typed debug info

In a debugger it's nice to inspect variables in their supposed type.

Can probably use unions to do this... probably wouldn't be as nice though.

** God knows what other optimisations

float4 v = [ 0,0,0,0 ]; // XOR v

etc...

I don't know what amount of this is achievable with libraries, but Walter seems to think this will all work much better in the language... I'm inclined to trust his judgement.