Since this is the Arc forum, I can link you to the Arc solution: http://arclanguage.org/item?id=3477 . It's a general way to set up infix notation for arithmetic, etc.
Just FYI, 'infix is not a keyword. (Arc doesn't really have keywords in the same way as other languages, the closest it has are words like 'quote, 'fn, and 'if, which need to be dealt with explicitly in the compiler. Things like 'def and '= which look like keywords in other languages are actually macros, allowing them to be (re)defined by the user inside of arc.)
Also note that there is an infix syntax (besides the custom DSL solution mentioned above), which would probably do what you want. (See http://arclanguage.org/item?id=2610.) You can
Note that using infix.arc, you don't even need an 'infix keyword around infix math. (This works as long as the object in functional position is a number.) Also note that the syntax of function calls is still exactly the same, it is just infix notation that is implemented.
Because infix notation doesn't interfere with the rest of the language, it actually used to be loaded by default on Anarki, but it was removed because it incurs a fairly hefty runtime overhead, even when using normal (prefix) math.
