2025-04-19 23:18:20 +02:00
2 changed files with 232 additions and 8 deletions
--- a/3
+++ b/3
@@ -58,7 +58,8 @@ APPENDIX: How to apply the Apache License to your work.

 To apply the Apache License to your work, attach the following boilerplate notice, with the fields enclosed by brackets "[]" replaced with your own identifying information. (Don't include the brackets!)  The text should be enclosed in the appropriate comment syntax for the file format. We also recommend that a file or class name and description of purpose be included on the same "printed page" as the copyright notice for easier identification within third-party archives.

-Copyright [yyyy] [name of copyright owner]
+Copyright [2023] [EndMove]
+Copyright [2025] [Varmix]

 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
--- a/README.md
+++ b/README.md
@@ -406,19 +406,236 @@ print(coroutine.resume(routine, 7, 8, 9)) -- 1+2+3 = '6'

 ### Error handling

-Lua allows low-level error handling with the `error` function and high-level error handling with the `assert` function. The `error` function raises an error and handles it with the `pcall` or `xpcall` function. The `assert` function checks a condition and raises an error if the condition is not met.
+Lua provides several core functions for error handling: `assert`, `error`, `pcall` (protected call), and `xpcall` (extended protected call), each offering different levels of control.  
+The examples below will explain and illustrate how each method is intended to be used.

-````lua
+#### assert
+
+`assert` is used to check a condition. If the result is `false` or `nil`, it triggers an error with a custom message.  
+It's especially useful when validating user input or enforcing preconditions.
+
+```lua
+local function isMajorUser(age)
+	assert(age >= 18, "You are not allowed to buy this item, you need to be 18 years old")
+end
+
+isMajorUser(15)
+-- Output : You are not allowed to buy this item, you need to be 18 years old !
+```
+
+#### error(message [, level])
+
+The `error` function allows you to manually raise an error, similar to `throw` in other languages. It immediately stops the current execution flow.  
+You can provide a custom error message, as well as a `level` parameter to control where the traceback starts in the call stack.
+
+Possible values for `level`:
+
+- **0**: No call stack information is shown.
+
+```lua
+error("Simple error without trace", 0)
+-- Result: Simple error without trace
+```
+
+- **1** *(default)*: The error appears at the exact place where `error` is called.
+
+```lua
+local function triggerError()
+    error("An error has occurred", 1)
+end
+
+triggerError()
+
+-- Result
+--[[
+lua: script.lua:2: An error has occurred
+stack traceback:
+    script.lua:2: in function 'triggerError'
+    script.lua:5: in main chunk
+]]
+```
+
+- **2**: The error appears at the place where the function **calling `error`** was itself called.
+
+```lua
+local function triggerError()
+    error("Error reported to caller", 2)
+end
+
+local function wrapper()
+    triggerError()
+end
+
+wrapper()
+
+-- Result
+--[[
+lua: script.lua:7: Error reported to caller
+stack traceback:
+    script.lua:7: in function 'wrapper'
+    script.lua:10: in main chunk
+]]
+```
+
+#### pcall (protected call)
+
+As its name suggests, `pcall` allows you to execute a function in **protected mode**, catching any potential error that might occur.  
+It acts similarly to a `try-catch` block found in other programming languages.
+
+The result of calling `pcall` returns two values, typically stored in two variables like `success` and `result`, though you can name them as you wish.
+
+- If the call succeeds:
+  - `success` will be `true`,
+  - `result` will contain the function’s returned value(s).
+
+- If an error occurs:
+  - `success` will be `false`,
+  - `result` will contain the error message.
+
+If the function does not return anything, `result` will be `nil`.
+
+```lua
+local function divideANumberByAnOther(a, b)
+	return a / b -- it would be better to validate parameters, but this is for example purposes
+end
+
+
+-------------------------------
+-- First scenario: error case
+-------------------------------
+local success, result = pcall(divideANumberByAnOther, 1, 0)
+
+if not success then
+	print("An error has occured :", result)
+end
+
+-- Output: An error has occured :
+
+
+-------------------------------
+-- Second scenario: valid case
+-------------------------------
+
+local success, result = pcall(divideANumberByAnOther, 10, 2)
+
+if success then
+	print("Result is :", result)
+end
+
+-- Output: Result is : 5



-- Throw an error if the first argument is false
-- the second argument is the error message.
-assert(type(firstvariable) = 'string', 'not a string')
+---------------------------------------------------------------------
+-- Third scenario: combine pcall with assert for critical operations
+---------------------------------------------------------------------

-- TODO to continue
+local function readFile(fileName)
+	local fileToRead = assert(io.open(fileName, "r"), "Impossible to read the file")
+	-- Continue processing if successfully opened
+	fileToRead:close()
+end

-````
+local success, result = pcall(readFile, "data.txt") -- providing a file name that doesn't exist
+
+if not success then
+	print("An error has occured :", result)
+end
+
+-- Output: An error has occured : Impossible to read the file
+
+-- Here we use assert to robustly manage errors: if the file cannot be opened, 
+-- assert triggers an error and immediately stops the program with the message.
+
+
+
+-----------------------------------------------------------------------
+-- Fourth scenario: pcall with a function that returns multiple values
+-----------------------------------------------------------------------
+local function sumAndProduct(a, b)
+	return a + b, a * b
+end
+
+local success, sum, product = pcall(sumAndProduct, 3, 4)
+
+if success then
+	print("Sum :", sum) -- 7
+	print("Product :", product) -- 12
+else
+	print("Error : ", sum) -- sum would contain the error message if one occurred
+end
+
+-- Reminder: pcall always returns two things:
+-- 1. A boolean indicating if the call was successful.
+-- 2. All values returned by the function if successful.
+```
+
+#### xpcall (extended protected call)
+
+`xpcall` is the big brother of `pcall`. It works in the same way but with an extra feature:  
+we can provide a **custom error handler function** that will be executed if an error occurs during the protected function call.
+
+This is especially useful when we want to customize how errors are displayed or logged, for example by adding stack traces or additional context.
+
+```lua
+local function errorHandler(err)
+    print("🔴 Error caught:", err)
+    print(debug.traceback("Stack trace:", 2))
+end
+
+local function riskyFunction()
+    print("🟢 In riskyFunction")
+    error("Something went wrong!")
+end
+
+local function wrapper()
+    print("🟡 Calling riskyFunction()")
+    riskyFunction()
+    print("🟡 After riskyFunction") -- never reached
+end
+
+print("1. Start")
+
+local success, result = xpcall(wrapper, errorHandler)
+
+print("2. Execution finished")
+print("3. Success:", success)
+print("4. Result:", result)
+
+-- Output:
+--[[
+1. Start
+🟡 Calling riskyFunction()
+🟢 In riskyFunction
+🔴 Error caught: Something went wrong!
+Stack trace:
+stack traceback:
+    script.lua:6: in function 'riskyFunction'
+    script.lua:11: in function 'wrapper'
+    ...
+2. Execution finished
+3. Success: false
+4. Result: nil
+]]
+
+--[[
+===========================
+debug.traceback Cheatsheet
+===========================
+
+debug.traceback([message], [level])
+
+- message (string) → optional message shown before the stack trace
+- level (number) → determines where the trace starts in the call stack:
+
+    level = 0 → shows EVERYTHING, including debug.traceback itself
+    level = 1 → (default) starts trace inside errorHandler() (not very useful)
+    level = 2 → starts trace at the point where the error actually occurred (e.g., riskyFunction)
+
+Recommended usage:
+    debug.traceback("Optional message", 2)
+]]
+```

 ### Modules

@@ -476,3 +693,9 @@ g()  -- Prints out '343', nothing printed before now.

 ````

+### Credits
+
+- EndMove - [contact@endmove.eu](mailto:contact@endmove.eu)
+- Varmix - [contact@varmix.fr](mailto:contact@varmix.fr)
+
+