error checking through pcall

Trapping and handling errors. example from a Well House Consultants training course
More on Trapping and handling errors. [link]

This example is described in the following article(s):
• Error trapping in Lua - no exceptions. - [link]

Source code: wonky Module: U111

--[[
In this program, the first block is the "control" - it works
well as the "number" variable is a function. In the second
block, we call a numeric value. "pcall" traps the error and
lets us handle it in our code, but if we call it direct (the
very last example), it's going to crash out with a Lua error
]]

-- ======== Calling a function

function number()
        return 54
        end

-- trap any error from a call to number
-- protected function call

lots,more = pcall(number)

-- so it's under programmer's control
print (lots, more)

lots = number()
print ("again")

-- =============== Trying to call a numeric value

number = 42

-- trap any error from a call to number
-- protected funcion call

lots,more = pcall(number)

-- so it's under programmer's control
print (lots, more)

lots = number()
print ("again")

--[[

[trainee@holt lm10]$ lua wonky
true 54
again
false attempt to call a number value
lua: wonky:33: attempt to call global 'number' (a number value)
stack traceback:
        wonky:33: in main chunk
        [C]: ?
[trainee@holt lm10]$

]]

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