Extensible infix operators

[John Hind <john.hind@...>]

I'm working on a calculator program which uses Lua as its expression 
evaluator. I'd like to be able to offer extensible infix operators so 
you'd be able to write something like:

c = a func b

where a and b are numeric variables or expressions and func is a 
function. This would be evaluated as:

c = func(a, b)

At the moment I plan doing this by pre-processing the formula strings, 
but it occurs to ask if MetaLua or Token Filters could be used to add 
this to the language? It would be easier to disambiguate expressions 
like this if I already know that a token represents a function taking 
two parameters.

Any thoughts?