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> It seems to be impossible to override arithmetic operators on
> strings.  One can for example set the __add metamethod, but
> it only gets called when at least one of the strings cannot be
> coerced to a number.  For example:
>    getmetatable''.__add = function(x,y) return x..y end
>    'a'+'b' --> 'ab', fine
>    '1'+'2' --> 3

In general, arithmetic metamethods are only called when Lua "does not
know what to do". Lua "does know what to do" with '1' + '2'.

(Probably the right thing to do would be to elliminate coersion from
strings to numbers altogether...)

-- Roberto