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On 28-Sep-06, at 5:53 PM, Glenn Maynard wrote:

On Thu, Sep 28, 2006 at 10:46:58PM +0000, David Given wrote:
arg = "5"
print (arg+0)

Likewise, some compiler sugar to convert to treat '+a' as '0+a' would be
easy, not involve any additional opcodes, and would optimise away to
nothing in most cases.

echo 'for i = 1,10000000 do local a = 5*(i); end' | time luac -l -
echo 'for i = 1,10000000 do local a = 5*(0+i); end' | time luac -l -

Lua's compiler doesn't do much (any?) optimization.

It could only optimize that by recognizing that i was a number; otherwise, 0+i could trigger an arbitrary metamethod. (The same comment applies to - -i). Here I think that use of tonumber() is better, particularly since tonumber can be used as a test:

i = tonumber(s)
if i then
  -- at this point i is known to be a number

If I understood your desire for "unary +" correctly, your needs would be satisfied if the lexer recognized + as the first character in a numeric lexeme, no? The use case did not seem to require the use of + as an operator.