Decisions with if

An if statement chooses whether a block of code should run:

if temperature > 30 then
    print("It is hot")
end

The condition between if and then must have type Boolean. Pop does not treat numbers, strings, objects, or nil as truthy or falsy values.

Choosing between two paths

Add else when the program should run another block if the condition is false:

if score > 9 then
    print("New high score")
else
    print("Keep trying")
end

Exactly one branch runs. Both finish at the shared end.

Testing several cases

An else block may contain another if:

if score > 89 then
    print("Excellent")
else
    if score > 59 then
        print("Passed")
    else
        print("Try again")
    end
end

The first true condition selects the message. Pop 0.1.0-rc.2 does not have a separate elseif keyword, so nested decisions use another if inside else.

Names declared in branches

Each branch is a scope. A local declared inside it is available only until that branch ends:

if authenticated then
    local message = "Welcome back"
    print(message)
end

-- message is no longer in scope

If a value will be needed after the decision, declare a local before the if and assign a same-typed value in each branch.