Lua/Functions

Lua modules based on the Scribunto/Lua extension are stored in resource pages using the Module: namespace. Each module uses a table to hold functions and variables, and that containing table is returned at the end of the module code. Functions are code structures used to encapsulate a series of statements that may be called as needed. This lesson will show you how to use functions in your scripts.

Prerequisites

This lesson assumes you have already completed the Loops lesson.

Create a Lua Script with Functions

To create a Lua script with functions:

1. Navigate to Module:Sandbox.
2. Clear all existing code.

   It's a sandbox. Everyone is free to play in the sandbox. But if you find another user is actively editing the sandbox at the same time, you may also use Module:Sandbox/Username, where Username is your Wikiversity username.

3. Add the following code and save the page:

local p = {}

local function toCelsius(f)
    return (f - 32) * 5 / 9
end

local function toFahrenheit(c)
    return c * 9 / 5 + 32
end

function p.functions()
    local temperature
    local result
	
    result = ';Fahrenheit to Celsius\n'
    for temperature = 0, 100, 10 do
        result = result .. ':' .. temperature .. ' °F is ' .. string.format('%.1f', toCelsius(temperature)) .. ' °C\n'
    end
 
    result = result .. ';Celsius to Fahrenheit\n'
    for temperature = 0, 100, 10 do
        result = result .. ':' .. temperature .. ' °C is ' .. string.format('%.1f', toFahrenheit(temperature)) .. ' °F\n'
    end
    return result
end

return p

Test Your Lua Script

To test your Lua script:

1. Navigate to either the Module_talk:Sandbox page, the Wikiversity:Sandbox page, or your own user or sandbox page.
2. Add the following code and save the page:

{{#invoke:Sandbox|functions}}

The result should be:

Fahrenheit to Celsius

0 °F is -17.8 °C

10 °F is -12.2 °C

20 °F is -6.7 °C

30 °F is -1.1 °C

40 °F is 4.4 °C

50 °F is 10.0 °C

60 °F is 15.6 °C

70 °F is 21.1 °C

80 °F is 26.7 °C

90 °F is 32.2 °C

100 °F is 37.8 °C

Celsius to Fahrenheit

0 °C is 32.0 °F

10 °C is 50.0 °F

20 °C is 68.0 °F

30 °C is 86.0 °F

40 °C is 104.0 °F

50 °C is 122.0 °F

60 °C is 140.0 °F

70 °C is 158.0 °F

80 °C is 176.0 °F

90 °C is 194.0 °F

100 °C is 212.0 °F

Understand Your Lua Script

To understand your Lua script toCelsius function:

1. local function toCelsius(f) declares a local function named toCelsius that accepts a single parameter f, which is the Fahrenheit temperature to be converted.

   Declaring the function as local prevents it from being called from outside the module.

2. return (f - 32) * 5 / 9 converts the Fahrenheit temperature into Celsius and returns the result.
3. end ends the function.

To understand your Lua script toFahrenheit function:

1. local function toFahrenheit(c) declares a local function named toFahrenheit that accepts a single parameter c, which is the Celsius temperature to be converted.

   Declaring the function as local prevents it from being called from outside the module.

2. return c * 9 / 5 + 32 converts the Celsius temperature into Fahrenheit and returns the result.
3. end ends the function.

To understand your Lua script functions function:

1. function p.functions() declares a function named functions.

   This function is not declared local, so it can be called from outside the module.

2. local and the following code defines the variables temperature and result. Both are nil.
3. result = ';Fahrenheit to Celsius\n' assigns a string literal value to the variable result.
4. for temperature = 0, 100, 10 do creates a loop code block that will vary the value of the variable temperature from 0 to 100 by 10.
5. toCelsius(temperature) calls the toCelsius function and passes in the current value of temperature as the temperature to be converted.
6. string.format() calls the string library format function to format the returned Celsius temperature.
7. '%.1f' indicates that the resulting format (%) should be a single decimal place (.1) floating point (f) value.
8. toFahrenheit(temperature) calls the toFahrenheit function and passes in the current value of temperature as the temperature to be converted.
9. string.format() calls the string library format function to format the returned Fahrenheit temperature.
10. '%.1f' indicates that the resulting format (%) should be a single decimal place (.1) floating point (f) value.
11. return result returns the current value of result as the result of the function.

It should be noted that this script makes use of three different function types:

• locally accessible functions (toCelsius, toFahrenheit)
• globally accessible functions (functions)
• library functions (string.format).

Conclusion

Congratulations! You've now created, tested, and understood a Lua script with functions. Continue on to the Tables lesson.

See Also

• Wikipedia: Subroutine

References

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Lua

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