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lazy operators / short circuit evaluation
Functions. example from a Well House Consultants training course
More on Functions. [link]
Source code: lazy Module: U106

--[[
In Lua, if a partial expression evaluates to true the
following section will NOT be evaluated if it follows
an or because the whole thing cannot be true.

If a partial expression evaluates to false, the following
section will NOT be evaluted if it follow an and because
the whole thing must be true.

If you find this a bit theoretic, try a real life example ...

If you're going to buy a kebab OR Fish and Chips and you find
the kebab shop open, you won't bother to carry on up the road
to the chippy because you have already met your needs.

If you require a hammer AND nails, but you can't find a
hammer, you won't go and search for the nails because even
if you find them, they're not going to be much use to you!

]]


function agelimit(incoming)
        return type(incoming) == "number" and incoming or 18
        end

print (agelimit(10))
print (agelimit(12))
print (agelimit("fourteen"))
print (agelimit(16))

--[[ ---------------------- Sample Output

[trainee@easterton u106]$ lua lazy
10
12
18
16
[trainee@easterton u106]$

]]

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