Re: lua-vec - Lua with vectors

["Alex Davies" <alex.mania@...>]

> Comments, bug reports and criticism of our unorthodox way are always 
> welcome!

A spot of criticism: adding another 8 bytes to the Value union is too much, 
imo.  Lots of stack copying on function calls etc, that will make an impact 
on the whole VM performance even when vectors aren't used.  Again, imo 
(really imo - I can't stress this enough) - vectors should be made GC.  Just 
copy the strings implementation - strings are plenty fast enough in Lua and 
are conceptually a 'vector' of characters, and this provides quick hashing 
benefits.  By doing it this way, adding vectors is low cost.

Also there's additional advantages - ie the length could become variable 
(why limit it to 4?), and changing to doubles wouldn't blow out the Value 
type.  Which would be a nice option to have as default, as mixing floats and 
doubles can cause all kinds of surprises for the unsuspecting.

I do like the decision to make them immutable.

And now on to dreaming territory:
imo the perfect vector extension to Lua would implement both vectors (tuple 
of numbers) and matrices (tuple of vectors of same dimension) - all the 
building blocks of a 3d app.  Throw in tuples for good measure (anything 
that is neither a matrix nor a vector).  All of these could be declared the 
same way, and let them be sorted out at runtime.

Perhaps hide the function call in a bit of parser higgery jiggery (say an 
OP_NEWTUPLE) and you have:

local tuple = [ "green eggs", "and ham" ]
local identitymatrix = [ [1, 0], [0, 1] ]
local vec = [ 1, 0, 0 ]
local fail_identitymatrix = [ vec, vec, vec ]

for i,v in ipairs(vec) do print(v) end

assert(type(tuple) == "tuple")
assert(type(vec) == "vector")
assert(type([[1], [2, 3]]) == "tuple")
assert(#identitymatrix == 2)
assert(#vec == 3)

(I'm aware this causes a parser nightmare when declaring tables in array 
form, ie { [1, 2], [2, 3] }, but I'm still dreaming here, maybe use <!!>?).

... and while you're at it throw in swizzles (newvec = vec.zzx), dot point 
and cross product operators (lets say .! and *!), perhaps vertices 
(collection of vectors) and vertexstrings (collection of vertices) and you 
have a pretty nifty language aimed at 3d graphics ;). Then you just need a 
genius (read: Mike Pall) to make a pixel shader/vertex shader runtime 
compiler (or cross compiler to hlsl) out of it, and... well, at this point I 
snapped back to reality.

But maybe some of that's doable..

- Alex