CODEWITHSUNDEEP
luaevaluation
user6245072
user6245072

Reputation: 2161

Why is the second instrution evaluated before the first one?

I was doing some calculations to use as the testcases for a question I'm going to post on PCCG Stack Exchange, and I noticed that in a piece of code like this:

for i = 0, 20 do
    io.write(i..": ")
    diff(i)
end

(where diff is a function which does some pretty heavy calculation and prints the result), the result of diff is first calculated and, only then, i: and the result of diff are printed.

But why is this happening? Shouldn't I see i: before and during the calculation, and the result of the calculation only after? Why is it waiting for diff to execute before?

I first noticed this using Luajit, but it also happens on vanilla Lua and even outside of a for loop.

Upvotes: 2

Views: 54

Answers (1)

Oleg V. Volkov
Oleg V. Volkov

Reputation: 22421

Just as with many other output functions in many other languages, io.write output is buffered. It is evaluated, it is just your output is now in intermediate buffer pending flushing or filling of this buffer. Add an io.flush() call if you need your data to go through right now.

Upvotes: 5

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